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Although there have been attempts to infer Neogene oceanic circulation patterns in the tropical Pacific on the basis of multiple marine proxies, oceanic circulation patterns across the early/middle Miocene boundary are still poorly understood despite paleoclimate having significantly changed during this interval. In this study, we reconstruct the changes in tropical oceanic circulation patterns in the Pacific across the early/middle Miocene boundary based on radiolarian assemblages obtained at Integrated Ocean Drilling Program Site U1335 in the eastern tropical Pacific. The radiolarian upwelling taxa increased during four intervals (18.4–18.1 Ma, 16.9–15.7 Ma, 15.2–14.6 Ma, 14.2–13.4 Ma). Radiolarian temperature index (RTI) was calculated using the relative abundances of the warm water (cluster B1) and cool water taxa (cluster B2) in order to evaluate relative temperature fluctuations of the surface water. The sea surface temperature index was relatively high from 16.8 to 16.0 Ma and gradually decreased from 16.0 to 14.6 Ma. Subsequently, the temperature index decreased stepwise at 13.9 and 13.4 Ma and became relatively low from 13.4 to 12.7 Ma. Comparison of the RTI record in the eastern tropical Pacific to the climatic index based on the benthic foraminiferal δ18O record shows that variability in the two records follows a roughly similar trend from the early to the middle Miocene. However, the sea surface temperature record does not indicate a sharp increase in warmth in the eastern tropical Pacific during the mid-Miocene climatic Optimum-1 (MMCO-1), as suggested by the benthic isotopic record. This is likely because of increased upwelling of cool, nutrient-rich water at this time. Beginning in the latest early Miocene (~ 17 Ma) radiolarian assemblages were dominated by different taxa in the eastern and western tropical Pacific. This pattern is interpreted as indicating a shallower thermocline in the east and a deeper thermocline in the west, based on the relative abundance of the upwelling taxa. There is an overall increasing trend in this difference since the latest early Miocene. We tie these events to the effective closure of the Indo-Pacific seaway and the development of a substantial western Pacific warm pool along with the development of a strong Equatorial Undercurrent.

In recent decades, the scientific ocean drilling community has prided itself in being able to achieve the full recovery of hundreds of meters of the sedimentary section through coring, allowing sci ...

Mercury stable isotopic compositions were determined for marine sediments from eight locations in the Arctic Ocean Basin. Mass dependent fractionation (MDF) and mass independent fractionation (MIF) of Hg stable isotopes were recorded across a variety of depositional environments, water depths, and stratigraphic ages. δ202Hg (MDF) ranges from −2.34‰ to −0.78‰; Δ199Hg (MIF) from −0.18‰ to +0.12‰; and Δ201Hg (MIF) from −0.29‰ to +0.05‰ for the complete data set (n = 33). Holocene sediments from the Chukchi Sea and Morris Jesup Rise record the most negative Δ199Hg values, while Pleistocene sediments from the Central Arctic Ocean record the most positive Δ199Hg values. The most negative δ202Hg values are recorded in Pleistocene sediments. Eocene sediments (Lomonosov Ridge) show some overlap in their Hg isotopic compositions with Quaternary sediments, with a sample of the Arctic Ocean PETM (56 Ma) most closely matching the average Hg isotopic composition of Holocene Arctic marine sediments. Collectively, these data support a terrestrially-dominated Hg source input for Arctic Ocean sediment through time, although other sources, as well as influences of sea ice, atmospheric mercury depletion events (AMDEs), and anthropogenic Hg (in core top samples) on Hg isotopic signatures must also be considered.

The anisotropy of magnetic susceptibility (AMS), or magnetic fabric, of marine sediments is related to depositional current strength; higher AMS values indicate stronger currents. We have collected a 3.1 m.y. record of AMS data from the abyssal silts of Drift 4 (Ocean Drilling Program Site 1101) on the Pacific margin of the Antarctic Peninsula. Spectral analyses of these data show strong, uniform, 100 k.y. and 400 k.y. power in-phase with minima in Earth’s eccentricity throughout the long record. However, significant variability related to the 40 k.y. period of obliquity is absent. The unchanging strong 100 k.y. power and the apparent absence of 40 k.y. variability in the AMS record are in contrast to the behavior of most other paleoclimatic proxies for late Pliocene and Pleistocene time.

The collision of India with Asia had a profound influence on Cenozoic topography, oceanography, climate, and faunal turnover. However, estimates of the time of the initial collision, when Indian continental crust arrived at the Transhimalayan trench, remain highly controversial. Here we use radiolarian and nannofossil biostratigraphy coupled with detrital zircon geochronology to constrain firmly the time when Asian-derived detritus was first deposited onto India in the classical Sangdanlin section of the central Himalaya, which preserves the best Paleocene stratigraphic record of the distal edge of the Indian continental rise. Deep-sea turbidites of quartzarenite composition and Indian provenance are replaced upsection by turbidites of volcano-plutoniclastic composition and Asian provenance. This sharp transition occurs above abyssal cherts yielding radiolaria of Paleogene radiolarian zones (RP) 4–6 and below abyssal cherts containing radiolaria of zone RP6 and calcareous shales with nannofossils of the Paleocene calcareous nannofossil zone (CNP) 7, constraining the age of collision onset to within the middle Paleocene (Selandian). The youngest U-Pb ages yielded by detrital zircons in the oldest Asia-derived turbidites indicate a maximum depositional age of 58.1 ± 0.9 Ma. Collision onset is thus mutually constrained by biostratigraphy and detrital zircon chronostratigraphy as 59 ± 1 Ma. This age is both more accurate and more precise than those previously obtained from the stratigraphic record of the northwestern Himalaya, and suggests that, within the resolution power of current methods, the India-Asia initial collision took place quasi-synchronously in the western and central Himalaya.

Microfossil-bound organic matter represents an important archive of surface ocean environmental information. Sedimentary nitrogen (N) isotope reconstructions of surface nitrate consumption and nitrogen source changes are made using fossil diatom (autotrophs) and planktic foraminiferal (heterotrophs)-bound organic matter with success. However, because diatoms and planktic foraminifera are poorly preserved and sedimentary organic matter content is near zero during the late Eocene, our ability to examine nutrient dynamics across this important climate transition is limited. Here we present new data exploring the use of N isotope records from radiolarian tests. A comparison of surface ocean nitrate and core top bulk and radiolarian N isotope values (as δ15N) from the equatorial Pacific indicates that radiolarian-N records δ15N variability with fidelity but that a significant offset exists between bulk sedimentary and diatom δ15N values and those measured from radiolarians (~7.1 ± 1.1‰). A downcore profile of radiolarian δ15N values is compared to siliceous microfossil assemblage changes across the Eocene-Oligocene boundary. Average of radiolarian-bound δ15N values is 0.5 ± 2.0‰, which, when corrected using the offset derived from the modern surface samples, suggests that the mean nitrogen isotopic composition of the early Cenozoic eastern Pacific was not significantly different from today. The overall trend, of decreasing δ15N values with decreasing export productivity, is consistent with either a regional decline in pelagic denitrification or a large-scale change in nutrient sources to the eastern equatorial Pacific (EEP), both linked to the cooling climate and changing intermediate water circulation. Decreasing/low δ15N values cooccur with high radiolarian species turnover at ~35.5 and 34 Ma, suggestive of a significant ecological change in the EEP, consistent with cooling and water mass distribution changes. The preliminary results suggest that radiolarian-bound organic nitrogen represents another promising archive and underscores the fact that the different microfossil fractions must be separated to ensure robust results.

Three distinct families of ATP:corrinoid adenosyltransferases (ACATs) exist that are capable of converting vitamin B12 derivatives to coenzyme B12 by catalyzing the thermodynamically challenging reduction of Co(II)rrinoids to form “super-nucleophilic” Co(I) intermediates. While the structures and mechanisms for the other two ACAT families have been studied extensively, little is known about the EutT enzymes beyond the fact that they exhibit a unique requirement for a divalent metal cofactor for enzymatic activity. In this study we have obtained compelling evidence that EutT converts cob(II)alamin to an effectively four-coordinate Co(II) species so as to facilitate Co(II) → Co(I) reduction. Intriguingly, EutT fails to promote axial ligand dissociation for the substrate analogue cob(II)inamide, a natural precursor of cob(II)alamin. This unique substrate specificity of EutT has important physiological implications.

CobA from Salmonella enterica (SeCobA) is a member of the family of ATP:Co(I)rrinoid adenosyltransferase (ACAT) enzymes that participate in the biosynthesis of adenosylcobalamin by catalyzing the transfer of the adenosyl group from an ATP molecule to a reactive Co(I)rrinoid species transiently generated in the enzyme active site. This reaction is thermodynamically challenging, as the reduction potential of the Co(II)rrinoid precursor in solution is far more negative than that of available reducing agents in the cell (e.g., flavodoxin), precluding nonenzymic reduction to the Co(I) oxidation state. However, in the active sites of ACATs, the Co(II)/Co(I) redox potential is increased by >250 mV via the formation of a unique four-coordinate (4c) Co(II)rrinoid species. In the case of the SeCobA ACAT, crystallographic and kinetic studies have revealed that the phenylalanine 91 (F91) and tryptophan 93 (W93) residues are critical for in vivo activity, presumably by blocking access to the lower axial ligand site of the Co(II)rrinoid substrate. To further assess the importance of the F91 and W93 residues with respect to enzymatic function, we have characterized various SeCobA active-site variants using electronic absorption, magnetic circular dichroism, and electron paramagnetic resonance spectroscopies. Our data provide unprecedented insight into the mechanism by which SeCobA converts the Co(II)rrinoid substrate to 4c species, with the hydrophobicity, size, and ability to participate in offset π-stacking interactions of key active-site residues all being critical for activity. The structural changes that occur upon Co(II)rrinoid binding also appear to be crucial for properly orienting the transiently generated Co(I) “supernucleophile” for rapid reaction with cosubstrate ATP.

There is general agreement that productivity in high latitudes increased in the late Eocene and remained high in the early Oligocene. Evidence for both increased and decreased productivity across the Eocene-Oligocene transition (EOT) in the tropics has been presented, usually based on only one paleoproductivity proxy and often in sites with incomplete recovery of the EOT itself. A complete record of the Eocene-Oligocene transition was obtained at three drill sites in the eastern equatorial Pacific Ocean (ODP Site 1218 and IODP Sites U1333 and U1334). Four paleoproductivity proxies that have been examined at these sites, together with carbon and oxygen isotope measurements on early Oligocene planktonic foraminifera, give evidence of ecologic and oceanographic change across this climatically important boundary. Export productivity dropped sharply in the basal Oligocene (~33.7 Ma) and only recovered several hundred thousand years later; however, overall paleoproductivity in the early Oligocene never reached the average levels found in the late Eocene and in more modern times. Changes in the isotopic gradients between deep- and shallow-living planktonic foraminifera suggest a gradual shoaling of the thermocline through the early Oligocene that, on average, affected accumulation rates of barite, benthic foraminifera, and opal, as well as diatom abundance near 33.5 Ma. An interval with abundant large diatoms beginning at 33.3 Ma suggests an intermediate thermocline depth, which was followed by further shoaling, a dominance of smaller diatoms, and an increase in average primary productivity as estimated from accumulation rates of benthic foraminifera.

Sedimentary sequences obtained from drilling during Integrated Ocean Drilling Program (IODP) Expedition 320/321, “Pacific Equatorial Age Transect (PEAT)” at eight sites (Sites U1331–1338) in the equatorial Pacific offer an ideal record for reconstructing the evolution of the ocean/climate system throughout the Cenozoic. The sediments drilled at Site U1335 record short-term events of paleoceanographic significance, including the early Miocene climatic optimum (MCO) and the middle Miocene climatic transition (MMCT). Abundant well preserved radiolarians were recovered from the lower Miocene radiolarian Zone RN2 through middle Miocene Zone RN5 at IODP Site U1335. A total of 46 radiolarian datum levels consisting of 20 first occurrences (FOs), 25 last occurrences (LOs), and one evolutionary transition (ET) was recognized within the studied interval at Site U1335. Of these datum levels, 36 radiolarian datum levels were directly tied to the geomagnetic polarity time scale (GPTS) across the early/middle Miocene boundary. The general magnitude of evolutionary change was estimated based on the total turnover rate (the sum of FOs and LOs per 0.5 m.y.) of tropical radiolarians, and two minor faunal turnovers of radiolarian species were recognized between 16.5 and 14.7 Ma and between 13.9 and 13.4 Ma. These faunal turnovers were associated with regional environmental changes such as the increased biological productivity in the equatorial Pacific during the MCO and the MMCT.

[1] The Eocene-Oligocene (E/O) boundary interval marks one of the largest and most rapid changes in climate during the last 50 Myr. Because of a very shallow calcium carbonate compensation depth in the Eocene, as well as the reworking of sediments and hiatuses in the boundary zone, it has also been one of the most difficult stratigraphic boundaries to study in deep water marine sections, especially in the Pacific Ocean. Recently, three drill sites have recovered complete sections of the E/O boundary interval in the tropical Pacific. A detailed study of these sections shows a series of pulses of reworked older radiolarians in the upper Eocene and lowermost Oligocene. The two largest pulses are coincident with the two sharp steps in carbon and oxygen isotope values that bracket the E/O boundary. Several smaller peaks in reworked material precede these two maxima. It is proposed that immixing of the older radiolarian species results from erosion and redeposition, possibly linked to pulses of new bottom water formation and the formation of a deep pycnocline.

Lake Nicaragua, the largest lake in Central America, is a promising site for paleolimnological study of past climate change, tectonic and volcanic activity, and pre-Columbian agriculture in the region. It is near the northern limit of the Intertropical Convergence Zone (ITCZ), which brings the rainy season to the tropics, so effects of decreasing precipitation due to southern migration of the ITCZ through the Holocene should be observable. Because fault zones and an active volcano lie within the lake, the long-term impact of tectonic and volcanic activity can also be examined. Finally, the fertile volcanic soils near the lake may have encouraged early agriculture. We analyzed diatoms, biogenic silica (BSi), total organic carbon (TOC), water content, volcanic glass, and magnetic susceptibility in a sediment core from Lake Nicaragua with eleven accelerator mass spectroscopy radiocarbon dates, spanning ~5,700 years. Sediment accumulation rates decreased from the bottom to the top of the core, indicating a general drying trend through the Holocene. An increase in eutrophic diatom abundance suggests that pre-Columbian agriculture impacted the lake as early as ~5,400 cal yr BP. Above a horizon of coarser grains deposited sometime between ~5,200 and 1,600 cal yr BP, planktonic diatoms increased and remained dominant to the top of the core, indicating that water depth permanently increased. Although magnetic susceptibility peaked and water content dipped at the coarse horizon, volcanic glass fragments did not increase, suggesting that the coarse horizon and subsequent increase in water depth were caused by tectonic rather than by volcanic activity. Decreased accumulation rates of BSi and TOC indicate that water became clearer when depth increased.

The EutT enzyme from Salmonella enterica, a member of the family of ATP:cobalt(I) corrinoid adenosyltransferase (ACAT) enzymes, requires a divalent transition metal ion for catalysis, with Fe(II) yielding the highest activity. EutT contains a unique cysteine-rich HX11CCX2C(83) motif (where H and the last C occupy the 67th and 83rd positions, respectively, in the amino acid sequence) not found in other ACATs and employs an unprecedented mechanism for the formation of adenosylcobalamin (AdoCbl). Recent kinetic and spectroscopic studies of this enzyme revealed that residues in the HX11CCX2C(83) motif are required for the tight binding of the divalent metal ion and are critical for the formation of a four-coordinate (4c) cob(II)alamin [Co(II)Cbl] intermediate in the catalytic cycle. However, it remained unknown which, if any, of the residues in the HX11CCX2C(83) motif bind the divalent metal ion. To address this issue, we have characterized Co(II)-substituted wild-type EutT (EutTWT/Co) by using electronic absorption, electron paramagnetic resonance, and magnetic circular dichroism (MCD) spectroscopies. Our results indicate that the reduced catalytic activity of EutTWT/Co relative to the Fe(II)-containing enzyme arises from the incomplete incorporation of Co(II) ions and, thus, a decrease in the relative population of 4c Co(II)Cbl. Our MCD data of EutTWT/Co also reveal that the Co(II) ions reside in a distorted tetrahedral coordination environment with direct cysteine sulfur ligation. Additional spectroscopic studies of EutT/Co variants possessing a single alanine substitution at either the His67, His75, Cys79, Cys80, or Cys83 position indicate that Cys80 coordinates to the Co(II) ion, while the additional residues are important for maintaining the structural integrity and/or high affinity of the metal binding site.

Quantitative faunal analyses of radiolarians were used to reconstruct paleoceanographic conditions spanning the interval from Zones RP8 (Early Eocene) to RP16 (Middle Eocene) in pelagic sequences recovered at Integrated Ocean Drilling Program (IODP) Site U1331 in the eastern equatorial Pacific Ocean. On the basis of relative abundance data from the low to high latitudes reported in the previous literature, paleoceanographic indices were identified: (1) species indicative of warmer conditions include Stylosphaera coronata coronata , Phormocyrtis embolum , Dendrospyris didiceros , Phormocyrtis cf. proxima , and Thyrsocyrtis triacantha ; (2) species indicative of cooler conditions include: the Lophocyrtis aspera group, the Lithocyclia ocellus group, Hexacontium sp. A, Hexacontium sp. B, Thecosphaerella glebulenta , and Lithelius sp. A. Two warming and at least six cooling events in the Early to Middle Eocene were identified from radiolarian assemblage variations. The paleoclimatic trends can be summarized as follows: warming in C23n.2n to C21r (~ 51.5–49.0 Ma), and C18n (40.2–39.0 Ma); cooling in C21r (48.5–47.8 Ma), lower C20r (46.2–45.2 Ma), top C20r to C20n (44.0–43.0 Ma), top C20n to C19r (43.0–41.7 Ma), C19n to C18r (41.7–40.2 Ma), and C18n.1n (39.0–38.5 Ma). These cooling events corresponded to the ELi and BLi events, which were identified in benthic foraminiferal δ 18 O of the Southern Ocean. In general, radiolarian and opal mass accumulation rates (MARs) in the eastern equatorial Pacific had higher values in cooling conditions during the Middle Eocene. The changes in biological productivity in the eastern equatorial Pacific were associated with cooling of tropical surface water. The change in relative abundance of radiolarians and CaCO 3 content at Site U1331 indicated that Middle Eocene carbonate events (carbonate accumulation events [CAEs]; Lyle et al., 2005) coincided with the cooling events of tropical surface water. At least CAE-2 and CAE-3 were associated with high biological productivity as well as cooling.

ATP:Co(I)rrinoid adenosyltransferases (ACATs) are enzymes that catalyze the formation of adenosylcobalamin (AdoCbl, coenzyme B12) from cobalamin and ATP. There are three families of ACATs, namely CobA, EutT and PduO. In Salmonella enterica, CobA is the housekeeping enzyme that is required for de novo AdoCbl synthesis and for salvaging incomplete precursors and cobalamin from the environment. Here, we report the crystal structure of CobA in complex with ATP, four-coordinate cobalamin, and five-coordinate cobalamin. This provides the first crystallographic evidence for the existence of cob(II)alamin in the active site of CobA. The structure suggests a mechanism in which the enzyme adopts a closed conformation and two residues, Phe91 and Trp93, displace 5,6-dimethylbenzimidazole (DMB), the lower nucleotide ligand base of cobalamin, to generate a transient four-coordinate cobalamin, which is critical in the formation of the AdoCbl Co-C bond. In vivo and in vitro mutational analysis of Phe91 and Trp93 emphasize the important role of bulky hydrophobic side chains in the active site. The proposed manner in which CobA increases the redox potential of the cob(II)alamin/cob(I)alamin couple to facilitate formation of the Co-C bond appears to be analogous to that utilized by the PduO-type ACATs, where in both cases the polar coordination of the lower ligand to the cobalt ion is eliminated by placing that face of the corrin ring adjacent to a cluster of bulky hydrophobic side chains.

With growing use of numerical models to forecast lake conditions under future climates and other stressors, paleo-events in the history of the Great Lakes have greater potential for relevance. Past events and history may extend records of observations, provide estimates of the sensitivity of the lake system to stressing conditions, and contribute scenarios for model validation. Here we describe four examples that hold promise for improving understanding of the present and future Great Lakes: 1) using an event of lake closure to derive climate-hydrology sensitivity, 2) extending the record of lake-level history by examining beach ridge sequences, 3) investigating sedimentary black bands to indicate past anoxia at the lakebed in deep basins, and 4) deriving evidence of lake process teleconnections with atmospheric circulation.

Water bodies, ancestral to the present lakes including Lake Huron, first appeared in the southern Great Lakes basin about 15,500 14C years (18,800 cal years) BP during the oscillatory northward retreat of the last (Laurentide) ice sheet from its maximum position south of the Great Lakes watershed. Glacial lakes, impounded by a retreating ice margin on their northern shores, were continuously present after 13,000 14C (15,340 cal) BP for 3000 14C (3900 cal) years. Drainage routings varied in time through the Erie and Michigan basins to the Mississippi River system, a probable source for colonizing aquatic organisms, then to the Ontario basin, and finally northeastward to the Ottawa River valley via the isostatically-depressed North Bay outlet by 10,000 14C (11,470 cal) BP. Water levels were generally low between 10,000 and 7500 14C (11,470 and 8300 cal) BP and may have risen several tens of metres for short periods due to overflow of meltwater from upstream subglacial reservoirs or from glacial lakes impounded by residual ice in the Hudson Bay watershed. About 8000 14C (8890 cal) BP glacial runoff bypassed the Great Lakes, and Huron basin waters descended into hydrologic closure under the influence of the early Holocene dry climate. With increasing precipitation and water supply about 7500 14C (8300 cal) BP the Huron water body again overflowed its North Bay outlet. Differential isostatic uplift (fastest to the north-northeast) raised this outlet and lake level relative to the rest of the basin. The lake finally overflowed southern outlets at Chicago and Port Huron-Sarnia by 5000 14C (5760 cal) BP (during the Nipissing highstand). Enhanced erosion of the latter outlet and continued differential uplift of the basin led to the present configuration of Lake Huron and Georgian Bay.

A 14-meter long pelagic clay core recovered at Marlin Rise (40°00.531′S, 154°2.601′W; 4775 m water depth) in the Southwest Pacific Basin contains a record of eolian dust deposited since the early Miocene. Downcore analysis of detrital minerals reveals a dominantly eolian signature with relatively constant proportions of quartz, feldspar and illite and trace amounts of chlorite, kaolinite and smectite, consistent with a continental (loess-like) source region. Fish tooth Sr isotope stratigraphy reveals the base of the core to be 17.5 Ma, with low sedimentation rates (

Data on sections drilled by DSDP and ODP in the Pacific have been compiled for 187 sites, 105 of which contain chert. The spatial pattern of siliceous deposits in the Pacific generally follows the pattern of biologic productivity. There is some evidence that enhanced vertical diffusivity in the ocean during the Eocene warm climate gave rise to siliceous deposits on and near bathymetric highs and basin margins. The most common occurrence of chert is in Eocene and older sections; however, cherts do occur in sections as young as 7 Ma in the sites investigated. Over half of the youngest chert occurrences in sedimentary sections are within 150 m of basement. Nearly all the chert occurrences on crust younger than 60 Ma are within 150 m of basement. The deficit in heat flow over ocean crust younger than 60 Ma is explained as the result of heat advection by hydrothermal waters circulating in the upper part of the ocean crust. These waters appear to dissolve biogenic silica and deposit it as chert in the lower parts of sedimentary sections. Diffusion of these waters into the lower sediment section is enhanced by small-scale faulting. This faulting may be associated with intra-plate stresses that develop during ridge jumps and reorientations of plate motion. The relatively warm bottom waters of the early Cenozoic may have also enhanced the dissolution of biogenic silica during hydrothermal circulation in the upper oceanic crust and basal sediment section.

EutT from Salmonella enterica is a member of a class of enzymes termed ATP:Co(I)rrinoid adenosyltransferases (ACATs), implicated in the biosynthesis of adenosylcobalamin (AdoCbl). In the presence of co-substrate ATP, ACATs raise the Co(II)/Co(I) reduction potential of their cob(II)alamin [Co(II)Cbl] substrate by >250 mV via the formation of a unique four-coordinate (4c) Co(II)Cbl species, thereby facilitating the formation of a “supernucleophilic” cob(I)alamin intermediate required for the formation of the AdoCbl product. Previous kinetic studies of EutT revealed the importance of a HX11CCX2C(83) motif for catalytic activity and have led to the proposal that residues in this motif serve as the binding site for a divalent transition metal cofactor [e.g. Fe(II) or Zn(II)]. This motif is absent in other ACAT families, suggesting that EutT employs a distinct mechanism for AdoCbl formation. To assess how metal ion binding to the HX11CCX2C(83) motif affects the relative yield of 4c Co(II)Cbl generated in the EutT active site, we have characterized several enzyme variants by using electronic absorption, magnetic circular dichroism, and electron paramagnetic resonance spectroscopies. Our results indicate that Fe(II) or Zn(II) binding to the HX11CCX2C(83) motif of EutT is required for promoting the formation of 4c Co(II)Cbl. Intriguingly, our spectroscopic data also reveal the presence of an equilibrium between five-coordinate “base-on” and “base-off” Co(II)Cbl species bound to the EutT active site at low ATP concentrations, which shifts in favor of “base-off” Co(II)Cbl in the presence of excess ATP, suggesting that the base-off species serves as a precursor to 4c Co(II)Cbl.

Corrinoid cofactors are critical components of the electron transport chain for many organohalide-respiring bacteria (OHRB). This chapter examines the synthesis and metabolism of corrinoids, with a focus on studies in bacteria that express reductive dehalogenases (RDases). We discuss the physical characteristics of corrinoids that make them distinct from one another, and provide examples of the various corrinoids isolated from OHRB. We provide a brief review of the synthesis, salvaging, and transport of corrinoids as it is currently understood in nondehalogenating model organisms. Wherever applicable, we draw parallels to the pathways present in OHRB. We present some recent examples of work studying the metabolism of corrinoids in mixed cultures of OHRB, and discuss how these bacteria may share and modify corrinoids at a community-based level.

J.L. Hough in 1962 recognized an erosional unconformity in the upper section of early postglacial lake sediments in northwestern Lake Huron. Low-level Lake Stanley was defined at 70 m below present water surface on the basis of this observation, and was inferred to follow the Main Algonquin highstand and Post-Algonquin lake phases about 10 14C ka, a seminal contribution to the understanding of Great Lakes history. Lake Stanley was thought to have overflowed from the Huron basin through the Georgian Bay basin and the glacio-isostatically depressed North Bay outlet to Ottawa and St. Lawrence rivers. For this overflow to have occurred, Hough assumed that post-Algonquin glacial rebound was delayed until after the Lake Stanley phase.

Pelagic clay of the east-central Pacific province is shown to be a mixture of three primary detrital components, reflecting continental source areas in Asia, North America, and Central and South America. Relative contributions from each source area are a function of geography, and this distribution appears to have remained constant over the past five million years, despite changing flux rates. A Q-mode factor analysis of downcore records for Pb, Sr, and Nd isotopes identified three factors that account for 98% of the total variance. These factors represent the radiogenic isotopic signatures of 1) late Cenozoic Asian dust, which dominates in the central North Pacific; 2) North American continental hemipelagic/eolian sources, restricted mainly to the easternmost North Pacific at ∼ 30 °N latitude; and 3) Central and South American sources, restricted to areas east of ∼ 100 °W longitude. South of the Intertropical Convergence Zone (∼ 6 °N), the Asian dust signature diminishes abruptly. We conclude that late Cenozoic Asian dust sources can be isotopically differentiated downcore from both North American and South and Central American sources in the east-central Pacific. This approach has a utility for identifying changes in long-term Cenozoic atmospheric circulation patterns.

Continuous Eocene through Oligocene sedimentary sedimentary sections were obtained at Holes 1218A, 1219A, and 1220A drilled during Leg 199 of the Ocean Drilling Program in the central equatorial Pacific. Quantitative analysis of radiolarian assemblages between the upper Eocene through lower Oligocene sedimentary successions revealed that major faunal changes of radiolarians occurred in the late Eocene (35.5–35.7 Ma; Subchron C16n1), around the Eocene/Oligocene boundary (33.7–33.8 Ma; upper Subchron C13r) and in the early Oligocene (30.9–31.3 Ma; uppermost Subchron C12r). The faunal change in the late Eocene is characterized by a stepwise decrease of tropical Eocene species and an increase in cosmopolitan, probably cool-water-tolerant, radiolarians; however, without a significant change in species diversity and radiolarian accumulation rates. The stratigraphic level of this late Eocene turnover came after the late Eocene impact event, and may have been more related to global cooling and associated oceanographic changes than to asteroid impact. The turnover around the Eocene/Oligocene boundary, corresponding to the Oi-1 event, is the most critical during the Eocene–Oligocene transition. Many biotic events such as a sudden drop of species diversity, an increase in the cosmopolitan radiolarian group, a large number of species turnovers, and a drop in radiolarian accumulation rates occurred at or just above this level. Together these indicators suggest a major restructuring of radiolarian assemblages from the high diversity Eocene fauna to a low diversity Oligocene one. The third turnover event within early Oligocene is represented by a replacement of dominant species with a sudden decrease in radiolarian accumulation rates. However, this Oligocene turnover is not consistent with other major δ18O isotope events, such as Oi-1b and Oi-2.

The global warming trend of the latest Oligocene was interrupted by several cooling events associated with Antarctic glaciations. These cooling events affected surface water productivity and plankton assemblages. Well-preserved radiolarians were obtained from upper Oligocene to lower Miocene sediments at Ocean Drilling Program (ODP) Leg 199 Sites 1218 and 1219 in the equatorial Pacific, and 110 radiolarian species were identified. Four episodes of significant radiolarian faunal changes were identified: middle late Oligocene (27.5 to 27.3 Ma), latest Oligocene (24.4 Ma), earliest Miocene (23.3 Ma), and middle early Miocene (21.6 Ma). These four episodes approximately coincide with increases and decreases of biogenic silica accumulation rates and increases in δ18O values coded as “Oi” and “Mi” events. These data indicate that Antarctic glaciations were associated with change of siliceous sedimentation patterns and faunal changes in the equatorial Pacific. Radiolarian fauna was divided into three assemblages based on variations in radiolarian productivity, species richness and the composition of dominant species: a late Oligocene assemblage (27.6 to 24.4 Ma), a transitional assemblage (24.4 to 23.3 Ma) and an early Miocene assemblage (23.3 to 21.2 Ma). The late Oligocene assemblage is characterized by relatively high productivity, low species richness and four dominant species of Tholospyris anthophora, Stichocorys subligata, Lophocyrtis nomas and Lithelius spp. The transitional assemblage represents relatively low values of productivity and species richness, and consists of three dominant species of T. anthophora, S. subligata and L. nomas. The characteristics of the early Miocene assemblage are relatively low productivity, but high species richness. The two dominant species present in this assemblage are T. anthophora and Cyrtocapsella tetrapera. The most significant faunal turnover of radiolarians is marked at the boundary between the transitional/early Miocene assemblages. We also reviewed changes in other microfossil assemblages in the low latitudes during the late Oligocene through early Miocene. The microfossil assemblages of major groups show sequential changes near the Oligocene/Miocene (O/M) boundary (23.8 Ma). Many extinction events and some first occurrences of calcareous nannofossils and many occurrences of radiolarians are found from about 24.8 to 23.3 Ma, and first occurrences of planktic foraminifers and diatoms followed from 23.2 through 22 Ma. Hence, the O/M boundary is identified as a significant level for microfossil evolutions.

A thick mound of fossiliferous sediments, reflecting high biogenic productivity at the Equator can be used to determine latitudinal motion of the Pacific lithospheric plate. Plate motion estimates based on the latitudinal movement of Equatorial facies are independent of paleomagnetic data and hotspot tracks and thus permit further testing of kinematic models. We have determined the northward motion of the Pacific Plate for the last 53 Myr based on the position of the paleoequator as shown by Equatorial sediment facies. Between 26 and 69 DSDP and ODP Sites sample the past 53 Myr in the tropical Pacific. Based on the mapped patterns of accumulation rates in these sites, we were able not only to determine the position of the paleoequator but also to estimate the Equatorial great circle and hence the relative position of the spin axis since the early Eocene. The northward motion of the Pacific Plate inferred from the change in latitude of dated Hawaiian Chain seamounts relative to the Hawaiian hotspot is consistently higher than that deduced from the analyses of Equatorial sediment facies. Such a difference results from a latitudinal shift of the Hawaiian hotspot during the last 53 Myr. All together, our observations and recent paleomagnetic results from the Detroit, Nintoku and Koko seamounts [J.A. Tarduno, R.A. Duncan, D.W. Scholl, R.D. Cottrell, B., Steinberger, T. Thordarson, B.C. Kerr, C.R. Neal, F.A. Frey, M. Torii, M., C. Carvallo. The Emperor Seamounts: Southward motion of the Hawaiian hotspot plume in Earth's mantle. Science 301 (2003) 1064–1069.] [1] are consistent with a progressive southward motion of the Hawaiian mantle plume since the Late Cretaceous. Our results suggest that the Hawaiian hotspot moved at ∼32 mm/yr to the SE during the past 43 million years and that the Pacific Plate moved ∼12° northward since 53 Ma at an average rate of 25 mm/yr.

The post-glacial history of the Great Lakes has involved several changes in lake levels throughout the latest Pleistocene and Holocene, resulting from the changing position of the retreating Laurentide ice sheet, outlet incision and isostatic rebound. The final lowering of lake levels occurred at approximately 7600 14C yr BP, after which lake levels began to rise again to the Nipissing highstand at approximately 4700 14C yr BP. During this time of rising lake levels, black bands of iron sulfide were being formed in the sediments of all five of the Great Lakes. These bands signify suboxic to anoxic conditions, at least within the sediments and possibly at the sediment-water interface, during the middle Holocene warm interval. During this interval, the climate was warmer and drier than present, possibly resulting in the occasional absence of seasonal turnover in the lakes. We examined a series of piston cores from northern Lakes Michigan and Huron and found that the black bands are correlatable among cores taken from within the same basin. The observation that the banding can be correlated suggests a basin-wide cause, near-bottom or sub-bottom anoxia in the northern Michigan and northern Huron sediments during the mid-Holocene warm period. The sedimentary and geochemical processes in the Great Lakes during the middle Holocene warm interval are good indicators of possible future scenarios for the lakes as a result of global warming, as 21st-century temperatures are predicted to reach similar levels due to increased concentrations of greenhouse gases.

Cenozoic pelagic (‘red’) clays of predominantly eolian and hydrogenous origin blanket much of the central North Pacific ocean basin. The eolian component is a key indicator of past paleoclimatic conditions; thus, Cenozoic atmospheric circulation can potentially be reconstructed through provenance studies of Pacific red clays, provided there are precise age controls. Methods commonly employed in the past to date red clay cores have included cobalt accumulation rates, ichthyolith biostratigraphy, magnetostratigraphy, and ichthyolith strontium isotope stratigraphy. The first two dating methods yield ages with large uncertainties, while magnetostratigraphy is only relevant to cores with accumulation rates in excess of 1 mm/kyr. Ichthyolith strontium isotope stratigraphy has shown promise as a chronological tool in marine studies, but has been only sparingly employed in the dating of marine red clay sequences. In this study, we present a complete age–depth profile for a large diameter piston core from the central North Pacific Ocean (EW9709 PC-01, 32.5°N, 141.2°W), consisting of 11 m of primarily wind-deposited dust. To generate this age–depth profile, strontium isotopic compositions were determined on fish teeth ichthyoliths previously cleaned of contaminants using a newly modified reductive cleaning procedure. Ages were determined by reference to the recently refined Sr isotope curve for Neogene seawater. Comparison with nearby giant piston core LL44-GPC3 reinforces the accuracy of our methods. The data for EW9709 PC-01 indicate a fairly constant sediment accumulation rate of ∼0.45 mm/kyr over most of the 24 Myr time period represented by this core.

A boxmodel of the Great Lakes is used to estimate meltwater flow into the North Atlantic between 8000 and 14,000 calendar years B.P. Controls on the model include the oxygen isotopic composition of meltwaters and lake waters as measured in the shells of ostracodes. Outflow rates are highest when oxygen isotopic values of the lake waters are most negative, denoting a maximum glacial meltwater component. Flow rates reach maximum values before the onset of the Younger Dryas and after it ends. These maxima appear to be correlative with the major meltwater pulses MWP 1A and 1B. Although the resumption of North Atlantic Deep Water formation may be tied to the reduction in ice sheet melting, neither the onset nor the end of the Younger Dryas, as recorded in the Greenland Ice Sheet Project (GISP2) records, appear tied to maxima in meltwater outflow from the Laurentide ice sheet.

A sediment core from northwestern Lake Huron contains a sequence of red and gray layered sediments that are postglacial and early Holocene glaciolacustrine varves. Two hundred and sixty four couplets were identified and measured using a newly developed image-analysis technique that produces records of seasonal and total varve thickness. On the premise that changes in varve thickness can serve as a proxy for climate variability, we use this information, along with oxygen-isotope records and seismic reflection profile data, to characterize a period immediately following the Younger Dryas. A time-series analysis of the thickness data was performed using two different techniques to characterize changes in spectral density that occur throughout the time span of the record. The results indicate that there are concentrations in variance that occur in the same frequency band as the quasi-periodic El Niño - Southern oscillation (ENSO) and the quasi-biennial oscillation (QBO). The effects of ENSO-like variability have not previously been documented in the postglacial and early Holocene of the Great Lakes region.

Lakes Baikal, Malawi and Tanganyika are the world's three largest rift valley lakes and are the classic modern examples of lacustrine rift basins. All the rift lakes are segmented into half-graben basins, and seismic reflection datasets reveal how this segmentation controls the filling of the rift basins through time. In the early stages of rifting, basins are fed primarily by flexural margin and axial margin drainage systems. At the climax of syn-rift sedimentation, however, when the basins are deeply subsided, almost all the margins are walled off by rift shoulder uplifts, and sediment flux into the basins is concentrated at accommodation zone and axial margin river deltas. Flexural margin unconformities are commonplace in the tropical lakes but less so in high-latitude Lake Baikal. Lake levels are extremely dynamic in the tropical lakes and in low-latitude systems in general because of the predominance of evaporation in the hydrologic cycle in those systems. Evaporation is minimized in relation to inflow in the high-latitude Lake Baikal and in most high-latitude systems, and consequently, major sequence boundaries tend to be tectonically controlled in that type of system. The acoustic stratigraphies of the tropical lakes are dominated by high-frequency and high-amplitude lake level shifts, whereas in high-latitude Lake Baikal, stratigraphic cycles are dominated by tectonism and sediment-supply variations.

Eight new radiocarbon ages, all determined by accelerator mass spectrometry, on modern (pre-bomb) mollusks have been added to similar data provided from three samples in the Lake Michigan and Huron basins. These data confirm the existence of a substantial hard water effect correction ranging from about 250 years to 500 years in these lakes. They also show that the magnitude of these corrections form a spatially coherent pattern that can be related to the pattern of outcrop of Paleozoic (radioactively inert) carbonates that surround the basins and the pattern of circulation within the basins.

Comparison of sedimentation patterns, basement subsidence, and faulting histories in the north and central basins of Lake Baikal aids in developing an interbasinal seismic stratigraphy that reveals the early synrift evolution of the central portion of the Baikal rift, a major continental rift system. Although there is evidence that the central and northern rift basins evolved at approximately the same time, their sedimentation histories are markedly different. Primary sediment sources for the initial rift phase were from the east flank of the rift; two major deltas developed adjacent to the central basin: the Selenga delta at the south end and the Barguzin delta at the north end. The Barguzin River system, located at the accommodation zone between the central and north basins, also fed into the southern part of the north basin and facilitated the stratigraphic linkage of the two basins. A shift in the regional tectonic environment in the mid Pliocene(?) created a second rift phase distinguished by more rapid subsidence and sediment accumulation in the north basin and by increased subsidence and extensive faulting in the central basin. The Barguzin delta ceased formation and parts of the old delta system were isolated within the north basin and on Academic Ridge. These isolated deltaic deposits provide a model for the development of hydrocarbon plays within ancient rift systems. In this second tectonic phase, the dominant sediment fill in the deeper and more rapidly subsiding north basin shifted from the flexural (eastern) margin to axial transport from the Upper Angara River at the north end of the basin.

International audience; Atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks; these feedbacks involve the erosion of silicate rocks and organic-carbon-bearing rocks. The integrated effect of these processes is reflected in the calcium carbonate compensation depth, which is the oceanic depth at which calcium carbonate is dissolved. Here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial Pacific Ocean. The carbonate compensation depth tracks long-term ocean cooling, deepening from 3.0-3.5 kilometres during the early Cenozoic (approximately 55 million years ago) to 4.6 kilometres at present, consistent with an overall Cenozoic increase in weathering. We find large superimposed fluctuations in carbonate compensation depth during the middle and late Eocene. Using Earth system models, we identify changes in weathering and the mode of organic-carbon delivery as two key processes to explain these large-scale Eocene fluctuations of the carbonate compensation depth.

United Launch Alliance (ULA) and their United States Air Force (USAF) Evolved Expendable Launch Vehicle (EELV) customer initiated operational flights of both the Atlas V and Delta IV launch vehicle families in 2002. Both Launch Vehicle families have provided 100% mission success since their respective inaugural launch and have demonstrated launch capability from both Vandenberg Air Force Base (VAFB) on the Western Range and Cape Canaveral Air Force station (CCAFS) on the Eastern Test Range. However, the current EELV fleet communications, tracking, and control architecture & technology, which date back to the origins of the space launch business, require support by a large and high cost ground footprint. The United States Air Force has embarked on an initiative known as Launch Enterprise Transformation (LET) that will significantly reduce Test Range Operations and Maintenance (O&M) cost by closing facilities and decommissioning ground assets. An important phase of the LET initiative is implementation of Global Positioning System (GPS) Tracking Unit developed by ULA and Space Vector Corporation on launch vehicles that use these ranges. GPS Metric Tracking (MT) is a way to leverage the existing GPS satellite base navigation system's capability in order to significantly reduce the costs of Test Range O&M. United Launch Alliance (ULA), in partnership with the U.S. Government, is engaged in a project plan to evolve the EELV fleet from dependence on ground based range assets to a Space Based Range operational concept. The initial phase was the development of the GPS Tracking Unit (GTU). ULA worked closely with the USAF to define and document the requirements for a GPS MT System for an EELV-class launch vehicle in accordance with the Range Commanders Council documentation (RCC 324–01T-EELV, Global Positioning and Inertial Measurements Range Safety Tracking Systems' Commonality Standard Tailored for EELV).1 The GTU provides precise launch vehicle position, velocity and timing information that can replace ground radar tracking resource functionality while utilizing Commercial Off The Shelf (COTS) components to reduce costs and increase capabilities. The availability of military grade components often limits system design and functionality. The GTU is designed to incorporate some of the most current commercial parts available that offer features not found in military components. These COTS components brought with them additional issues due to a lack of performance data in the launch vehicle environment for these new components. Space Vector utilized a stackable, modular design in developing the GTU for EELV. This approach allows for changes and upgrades to components within a specific module without adversely affecting the entire unit. The modular approach to the GTU design also allowed Space Vector to provide additional interfaces to accommodate both Atlas V and Delta IV unique power and ground interfaces into a single unit eliminating the need to develop separate configurations for each vehicle within the EELV family. The GTU also took advantage of an existing COTS receiver and processor that were ruggedized for the launch vehicle environments. The GTU completed all qualification testing in May 2011 and is currently in production. This paper summarizes the design approach, COTS issues, physical parameters and functional performance capabilities of the EELV GPS Tracking Unit. The implementation of COTS components in a launch vehicle environment required creating new methodologies and test processes to ensure reliability.

To reconstruct the climate history of the equatorial Pacific, one major objective of the Pacific Equatorial Age Transect (PEAT) program is to compile a Cenozoic megasplice that integrates all available bio-, chemo-, and magnetostratigraphic data including key records from Ocean Drilling Program (ODP) Leg 199. In order to do so, extended postcruise refinements of the shipboard composite depth scales and composite records are required. Here, we present a revised depth scale of Integrated Ocean Drilling Program (IODP) Expedition 320 Sites U1331, U1332, U1333, and U1334 as well as Leg 199 Sites 1218, 1219, and 1220. The revised composite records were used to perform site-to-site correlation and integration of Leg 199 and Expedition 320 sites. Based on this decimeter-scale correlation, a high-resolution integrated paleomagnetic, calcareous nannofossil, and radiolarian stratigraphy for the equatorial Pacific is established that covers the time from 20 to 40 Ma. This sedimentary compendium from the equatorial Pacific will be the backbone for paleoceanographic reconstructions for the late Paleogene.

Seismic reflection profiling and piston coring identified seismic reflectors in northern Lake Huron and Georgian Bay linked with unconformities caused by at least six reductions in lake level. In ascending stratigraphic order, these lowstands occurred at about 11 200 BP, associated with the Kirkfield outlet from early Lake Algonquin; 10 200 – 9900 BP, associated with the post-Algonquin lake level fall; 9800 – 9050 BP, the most extreme lowstand, associated with the main Stanley – Hough draw down; and 7800 – 7450 BP. The concomitant highstands are Lake Algonquin, from about 11 200 – 10 200 BP; early Lake Mattawa, between 9600 and 9350 BP; the main Mattawa phase, 9050–7800 BP; and the Nipissing highstand, at about 4700 BP. Isotopic and paleoecological data show that all of the lowstands are characterized by cold, dilute, and isotopically very light (< −20‰) waters from the melting Laurentian ice cap. Highstands, on the other hand, are characterized by higher dissolved solid concentrations and a much smaller meltwater component. Oxygen isotope values of the waters in these lakes were −15 to −17‰ in Lake Algonquin, −13 to −14‰ for the early and middle Mattawa stages, −9 to −8‰ for the main Mattawa stage, and −7‰ for modern waters. This association of lowstands and not highstands with isotopically light waters is a new contribution to early Holocene hydrology of the Great Lakes. The Younger Dryas cool episode is coeval with the Lake Algonquin highstand and a younger cool episode is generally coeval with the Mattawa highstand. This supports the hypothesis of C.F.M. Lewis and T.W. Anderson that these large cold lakes were responsible for regional cooling during the early Holocene.

Five seismic reflectors in the basinal sedimentary section have been identified as representing erosional surfaces in shoaler regions of the lake basins and can be traced throughout most of the study area. The reflectors representing these erosional surfaces, and their conformable equivalents in the deep lake basins, are caused by intervals of coarser grain size in the sediments and are thought to represent lowering of lake levels prior to, and following, the Main Algonquin highstand (about 10.2 – 11.0 ka). These reflectors are used to define seismic sequences in the postglacial sedimentary fill of the basins. Two additional erosional surfaces, which closely follow the initial fall of the Main Algonquin lake level, are most clearly seen in thicker sections found in the northern part of the basins. The two oldest (pre-Main Algonquin) sequences appear to onlap highs and fill in lows within the basins, whereas the younger sequences (associated with the Main Algonquin through Mattawa times) tend to drape the topography and show little difference in thickness between the lows and their adjacent highs. The most recent sedimentary sequence represents deposition occurring since about 7.5 ka. It laps out against topographic highs and leaves older sequences exposed at the lake floor in many areas. The most pronounced erosional surfaces are associated with the Light Green and the Light Blue sequence boundaries. The Light Green sequence has a pair of coarser layers at its top, which are dated at 9.6 – 9.8 ka and 9.05 – 9.2 ka. The coarser interval at the top of the Light Blue sequence is dated at 7.45 – 7.80 ka. These layers are thought to mark maximum lake level lowstands and to represent the times of Ottawa–Marquette to latest Mattawa lake level fluctuation.

United Launch Alliance (ULA) and their United States Air Force (USAF) Evolved Expendable Launch Vehicle (EELV) customer initiated operational flights of both the Atlas V and Delta IV launch vehicle families in 2002. Both Launch Vehicle families have provided 100% mission success since their respective inaugural launch and have demonstrated launch capability from both Vandenberg Air Force Base (VAFB) on the Western Range and Cape Canaveral Air Force station (CCAFS) on the Eastern Test Range. However, the current EELV fleet communications, tracking, & control architecture & technology, which date back to the origins of the space launch business, require support by a large and high cost ground footprint. The United States Air Force has embarked on an initiative known as Launch Enterprise Transformation (LET) that will significantly reduce Test Range Operations and Maintenance (O&M) cost by closing facilities and decommissioning ground assets. An important phase of the LET initiative is implementation of Global Positioning System Metric Tracking (GPS MT) on launch vehicles that use these ranges.

[1] Benthic foraminiferal stable carbon isotope records from the South Atlantic show significant declines toward more “Pacific-like” values at ∼7 and ∼2.7 Ma, and it has been posited that these shifts may mark steps toward increased CO2 sequestration in the deep Southern Ocean as climate cooled over the late Neogene. We generated new stable isotope records from abyssal subantarctic Pacific cores MV0502-4JC and ELT 25-11. The record from MV0502-4JC suggests that the Southern Ocean remained well mixed and free of vertical or interbasinal δ13C gradients following the late Miocene carbon shift (LMCS). According to the records from MV0502-4JC and ELT 25-11, however, cold, low δ13C bottom waters developed in the Southern Ocean in the late Pliocene and persisted until ∼1.7 Ma. These new data suggest that while conditions in the abyssal Southern Ocean following the LMCS were comparable to the present day, sequestration of respired CO2 may have increased in the deepest parts of the Southern Ocean during the late Pliocene, a critical period for the growth and establishment of the Northern Hemisphere ice sheets.

Strontium and neodymium radiogenic isotope ratios in early to middle Eocene fossil fish debris (ichthyoliths) from Lomonosov Ridge (Integrated Ocean Drilling Program Expedition 302) help constrain water mass compositions in the Eocene Arctic Ocean between ∼55 and ∼45 Ma. The inferred paleodepositional setting was a shallow, offshore marine to marginal marine environment with limited connections to surrounding ocean basins. The new data demonstrate that sources of Nd and Sr in fish debris were distinct from each other, consistent with a salinity-stratified water column above Lomonosov Ridge in the Eocene. The 87Sr/86Sr values of ichthyoliths (0.7079–0.7087) are more radiogenic than Eocene seawater, requiring brackish to fresh water conditions in the environment where fish metabolized Sr. The 87Sr/86Sr variations probably record changes in the overall balance of river Sr flux to the Eocene Arctic Ocean between ∼55 and ∼45 Ma and are used here to reconstruct surface water salinity values. The ɛNd values of ichthyoliths vary between −5.7 and −7.8, compatible with periodic (or intermittent) supply of Nd to Eocene Arctic intermediate water (AIW) from adjacent seas. Although the Norwegian-Greenland Sea and North Atlantic Ocean were the most likely sources of Eocene AIW Nd, input from the Tethys Sea (via the Turgay Strait in early Eocene time) and the North Pacific Ocean (via a proto-Bering Strait) also contributed.

[2] The Eocene biosiliceous oozes of the tropical Pacific are an easily recognizable sediment type having a reddish brown color and sugary texture. These sediments are dominated by radiolarian tests, with traces of terrigenous debris, hydrothermal oxides, a few diatoms and little if any carbonate. The paucity of carbonate is a result of the very shallow Pacific calcite compensation depth (CCD) of the Eocene (3300 m) [Rea and Lyle, 2005, and references therein]. The dominance of radiolarian tests over those of diatoms is an enigma in that diatoms usually dominate siliceous-rich sediments of the Oligocene and Neogene. The opal-rich character of these Eocene sediments is commonly associated with the development of cherts within the sections. [3] These unusual characteristics of Eocene radiolarian oozes have prompted some authors to puzzle over how so much silica could have been delivered to the sea floor during

Stable isotope analysis was performed on the structural carbonate of fish bone apatite from early and early middle Eocene samples (∼55 to ∼45 Ma) recently recovered from the Lomonosov Ridge by Integrated Ocean Drilling Program Expedition 302 (the Arctic Coring Expedition). The δ18O values of the Eocene samples ranged from −6.84‰ to −2.96‰ Vienna Peedee belemnite, with a mean value of −4.89‰, compared to 2.77‰ for a Miocene sample in the overlying section. An average salinity of 21 to 25‰ was calculated for the Eocene Arctic, compared to 35‰ for the Miocene, with lower salinities during the Paleocene Eocene thermal maximum, the Azolla event at ∼48.7 Ma, and a third previously unidentified event at ∼47.6 Ma. At the Azolla event, where the organic carbon content of the sediment reaches a maximum, a positive δ13C excursion was observed, indicating unusually high productivity in the surface waters.

[1] The Pacific Ocean likely exerted the greatest marine influence on climate during the greenhouse interval of the Paleogene. The first step toward assessing the role of Pacific deepwater circulation in global heat transport is a comprehensive reconstruction of deepwater mass composition and circulation patterns. We present new deepwater mass Nd isotope data from ODP Leg 199 Sites 1215, 1217, 1219, and 1221 to augment the existing coverage provided by ferromanganese crust and fossil fish debris data. The new data corroborate the notion that the Pacific Ocean operated in a bimodal pattern with deepwater sources in both the Southern Ocean and North Pacific for much of the early to middle Paleogene. In addition, the data indicate that there was little to no influence of Atlantic waters on the deepwater composition of the tropical Pacific. The available deepwater Nd isotope data provide refined constraints on the geographic and depth range of influence of both a Southern Ocean and North Pacific deepwater mass. From ∼65 to ∼45 Ma, the deep tropical Pacific was the mixing location of deep waters sourced from the Southern Ocean and the North Pacific. The Southern Ocean deepwater mass extended from ∼1800 m to abyssal depths. Until 53.6 Ma it circulated northward in the western Pacific at least as far as the paleolocation of Fe-Mn Crust CLD01 (∼5°N paleolatitude) and in the eastern portion of the Pacific as far as Site 1215 (∼10°N paleolatitude). A North Pacific deepwater mass extended from at least ∼2400 m to 2900 m water depth from ∼65 to 54 Ma, south to Shatsky Rise (paleolatitude ∼10–15°N), and possibly as far as Site 1215, 700 km to the south of Shatsky Rise Sites 1209 and 1211.

[1] A recent expedition to the equatorial Pacific surveyed over 60,000 km2 of seafloor using swath map imaging and high-resolution seismic profiling. This survey revealed the common occurrence of large pits in the biogenic sediments that are usually associated with basement highs. The pits range in size up to a few kilometers across and are on the order of 50 m – 100 m deep. They were found on seafloor ranging in age from 15 Ma to 55 Ma, with overlying sediment cover up to 500 m thick. We link their origin with hydrothermal discharge through conduits created by differential compaction and fracturing over basement highs and by basement faulting that penetrates the overlying sediments. Although carbonate dissolution is likely to be associated with the formation of the pits, their occurrence shows no consistent relationship with the present calcite compensation depth (CCD).