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Paleoceanographic changes in response to Holocene climate variability in Bigo Bay, west Antarctic Peninsula (WAP) were reconstructed through geochemical, isotopic, sedimentological, and microfossil analysis. Core WAP13-GC47 is composed of 4 lithologic units. Unit 4 was deposited under ice shelf settings. Unit 3 represents the mid-Holocene open marine conditions. Unit 2 indicates lateral sediment transport by a glacier advance during the Neoglacial period. The chronological contrast between the timing of open marine conditions at core WAP13-GC47 ( ca . 7060 cal. yr BP at 540 cm) and the ages of calcareous shell fragments ( ca . 8500 cal. yr BP) in Unit 2b suggests sediment reworking during the Neoglacial period. Unit 1 was deposited during the Medieval Warm Period (MWP) and the Little Ice Age (LIA). Surface water productivity, represented by biogenic opal and total organic carbon (TOC) concentrations, increased and bulk δ 15 N (nitrate utilization) decreased during the warmer early to middle Holocene and the MWP. In contrast, surface water productivity decreased with increased bulk δ 15 N during the colder Neoglacial period and LIA in Bigo Bay. The nitrate utilization was enhanced during cold periods in association with strong surface water stratification resulting from increased sea ice meltwater discharge or proximity to an ice shelf calving front in Bigo Bay. Reduced nitrate utilization during warm periods is related to weak stratification induced by less sea ice meltwater input and stronger Circumpolar Deep Water influence. [ABSTRACT FROM AUTHOR]

Constraining the role of microbes in the structural iron (Fe) reduction of iron-bearing minerals improves our understanding of sediments and ice sheets as a source of dissolved Fe (dFe) to the oceans. However, bio-mediated structural Fe-reduction has yet to be studied in cryospheric environments. Here, we show that the Fe reducing psychrophile bacterium Shewanella vesiculosa, isolated from sea ice in Antarctica, reduced structural Fe in nontronite (NAu-2) and maghemite (γ-Fe 2 O 3), common mineral phases in glacial ice, and marine sediments in Antarctica, during two freeze–thaw cycles (−10 °C to +15 °C), resulting in the release of dFe. The modification of turbostratically disordered nontronite (ferric iron dominant phase) to discrete ordered illite-like structure (ferrous iron dominant phase), and the aggregation of altered small maghemite particles with neoformation of vivianite (Fe 3 (PO 4) 2 ·nH 2 O) indicated the microbially induced reductive dissolution of nontronite and maghemite, respectively. The biotic Fe-reduction gradually decreased and ceased as the temperature approached freezing (−8 °C), however the rection reactivated in the thawing cycle (−7 to +15 °C). No discernable biotic Fe-reduction was measured for either mineral under freezing conditions, suggesting that temperature limits the activity of the microbes. Further, and regardless of temperatures during two freeze–thaw cycles, Fe-reduction was not observed in abiotic control. Overall, these results highlight the importance of microbially induced Fe reduction during seasonal freeze–thaw cycles of ice and sediments in continuous supplying bioavailable dFe to cryospheric environments and the often Fe-limited polar oceans. [ABSTRACT FROM AUTHOR]

To understand past changes in ocean–cryosphere interactions in the Southern Ocean off the Antarctic Peninsula, multi-proxy analyses of three sediment cores located off Elephant Island were used to reconstruct changes in paleoproductivity, nutrient utilization, bottom current intensity, and iceberg calving since the last glacial period. The glacial period was characterized by low surface water productivity with high nutrient utilization, indicating surface water stratification. During the deglaciation, surface water productivity increased with decreasing nutrient utilization, implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing Antarctic Circumpolar Current (ACC) influence as fronts migrate southward with warming. Abundant occurrence of grains >1 mm during the deglacial period indicates rapid ice sheet retreat with large-scale melting and calving. During the glacial period, however, coarse silt–fine sand-sized fraction represented ice-rafted debris (IRD). The different IRD grain size characteristics are thought to be related to the IRD source material characteristics. Regardless of IRD input, the running downcore correlation (5 to 9-point) between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current. However, the cross plot of them showed different temporal relationships. Sediments were sorted by the ACC and southwestward flowing bottom current. Along with southward migration of fronts and the ACC, southwestward flowing bottom current influence diminished, whereas the ACC influence increased particularly from 7 ka. Our results indicate that the sedimentary processes in the Scotia Sea largely depend on the regional interactions between the ocean and the cryosphere. • Deglacial productivity increase is due to increased nutrient supply as sea ice retreats. • Productivity and nutrient utilization decreased from 7 ka due to a deepening of the MLD. • The ACC kept enhancing from 7 ka with southward migration. • IRD grain-size characteristics are different between glacial and deglacial periods. • IRD grains >1 mm occurred more abundantly during the deglacial period. [ABSTRACT FROM AUTHOR]

Accelerating ocean-driven basal melting of Antarctic ice shelves in recent decades has implications for sea level rise and global overturning circulation. Here, we reconstruct oceanographic conditions at the confluence of the Ross Sea and the Southern Ocean by analyzing a multi-proxy Holocene marine sedimentary record collected from Robertson Bay. A ramped pyrolysis oxidation radiocarbon age-depth model provides a timeline for glacial behavior and oceanographic changes over the last 6700 years. The diatom assemblage, magnetic susceptibility, grain size, total organic carbon and nitrogen, trace elements, and bulk δ13C are used as proxies for changing ocean and glacial conditions, which we interpret in the context of modern oceanographic measurements. Our record shows evidence of persistent ice cover in the northwestern Ross Sea during the Antarctic mid-Holocene climate optimum (ca. 5 cal kyr BP). Based on this observation, we suggest that meltwater and iceberg discharge associated with ice sheet retreat in the Ross Sea region altered local oceanography during the mid-Holocene. The onset of modern style oceanographic conditions in Robertson Bay occurred at ca. 4 cal kyr BP. Stable late Holocene conditions in are punctuated by a period of enhanced polynya activity and upwelling of nutrient rich Circumpolar Deep Water ca. 0.8 cal kyr BP and an increase in the seasonal duration of sea ice after 0.7 cal kyr BP, during the Little Ice Age. The response of the marine environment in Robertson Bay to mid-Holocene ice sheet retreat and natural climate variability during the last millennium underscores the sensitivity of the Antarctic ice-ocean interface to projected changes in coming decades. • First Holocene paleoceanographic record from Robertson Bay, Ross Sea, Antarctica. • Mid-Holocene ice sheet retreat supported persistent ice cover ca. 5 cal kyr BP. • Enhanced polynya activity and upwelling of CDW ca. 0.8 cal kyr BP. • The seasonal duration of sea ice increased after 0.7 cal kyr BP, during the Little Ice Age. • Antarctic ice-ocean interface is sensitive to subtle changes in GMT, SAM, and ENSO. [ABSTRACT FROM AUTHOR]

We measured meteoric 10 Be variation throughout a marine sediment core from the Larsen B embayment (LBE) of the Antarctic Peninsula, and collected in situ 10 Be and 14 C exposure ages on terrestrial glacial deposits from the northern and southern margins of the LBE. We use these data to reconstruct Last Glacial Maximum (LGM) to present deglaciation and ice shelf change in the LBE. Core sedimentary facies and meteoric 10 Be data show a monotonic progression from subglacial deposits to sub-ice-shelf deposits to open-marine conditions, indicating that its collapse in 2002 was unprecedented since the LGM. Exposure-age data from the southern LBE indicate 40 m of ice surface lowering between 14 and 6 ka, then little change between 6 ka and the 2002 collapse. Exposure-age data from the northern LBE show a bimodal distribution in which clusters of apparent exposure ages in the ranges 4.9–5.1 ka and 1.0–2.0 ka coexist near 50 m elevation. Based on these results, other published terrestrial and marine deglaciation ages, and a compilation of sea bed imagery, we suggest a north-to-south progression of deglaciation in the northeast Antarctic Peninsula in response to Holocene atmospheric and oceanic warming. We argue that local topography and ice configuration inherited from the LGM, in addition to climate change, are important in controlling the deglaciation history in this region. [ABSTRACT FROM AUTHOR]

The rare earth element (REE) composition of a 4.96 m-long sediment core retrieved from the Hanon paleo-maar in Jeju Island, Korea was studied to investigate the East Asian monsoon variations during the latest Pleistocene to early Holocene (22,300–9000 cal BP). The studied paleo-maar core sediment has two restricted source materials with distinctively different geochemical signatures: Asian dust blown from central Asia (especially northern China and Mongolia) and basement rock composed of trachybasalt. The REE characteristics of sediments depend on the relative contribution of these two sources and thus can be used to delineate the monsoon climate in Jeju Island. The proportion of Asian dust generally decreased gradually from 67% at 22,300 cal BP, indicative of progressive weakening of the winter monsoon strength in central Asia. Integration of the REE data with TOC and MS records reveals that the summer monsoon strength in Jeju Island decreased from 22,300 cal BP until the last glacial maximum at 18,000 cal BP, and then increased to 14,000 cal BP. The abrupt intensification of the summer monsoon occurred from 14,000 to 13,300 cal BP, followed by the weakened summer monsoon from 13,300 to 11,000 cal BP, in anti-phase with the strengthened winter monsoon in central Asia. In the early Holocene, Jeju Island experienced further intensified summer monsoon strength. [ABSTRACT FROM AUTHOR]

Abstract: Textural and stable isotopic records from the absolute-dated stalagmite of the Daeya Cave (DY-1) provide new insights into the climatic evolution of the Korean Peninsula during the Holocene and Eemian climatic optima. The stalagmite yielded ages of 8572 ± 227 to 5907 ± 158 and 1,23,456 ± 535 to 1,19,837 ± 1089 years, which coincide with the Holocene and Eemian climatic optima, respectively. The stalagmite’s δ13C record closely resembles previously reported Chinese speleothem δ18O data. Thus it can be suggested that textural and geochemical results of the DY-1 reflect East Asian monsoon intensity, which is forced by summer insolation patterns in the northern hemisphere. Lighter carbon isotopic compositions, well-developed fibrous calcite crystals, and their relatively faster growth rate in the stalagmite sample are interpreted to reflect the warmest and wettest climate conditions of the Holocene and Eemian interglacials. Both climatic optima took place when insolation was decreasing from its maximum level, temperature in Greenland was highest, and sea level approached its maximum level. These climatic optima also coincide with decreasing Antarctic temperatures. Compared the DY-1 data to other proxies, it is suggested that the Holocene and Eemian climatic optima developed through a balance among boreal insolation, monsoon intensity, and sea level (also continental ice volume), which are the main climatic forcing factors in the northern hemisphere. These trends also follow the bi-polar seesaw mechanism as previously described. [Copyright &y& Elsevier]

The post-Last Glacial Maximum (LGM) deglaciation of Antarctica holds important clues for understanding past environmental changes and predicting future changes in the Antarctic Ice Sheet. Cosmogenic nuclide exposure dating of glacial erratics documents the spatial and temporal glacier changes during the most recent deglaciation. We collected 55 erratic cobbles from the eight glaciated benches on Inexpressible Island, which is at the terminal area of Priestley Glacier, Terra Nova Bay, Victoria Land, to elucidate its post-LGM deglaciation pattern. Analyses of the 10Be ages and 26Al/10Be ratios suggest that Priestley Glacier underwent ∼254 m of lowering during the mid-Holocene, between 8.9 and 5.9 ka. This lowering rate (∼0.09 m a−1) is faster than those observed along other Victoria Land outlet glaciers to the north (Tucker and Aviator), but slower than the one to the south (Mackay). The post-LGM lowering of these outlet glaciers was triggered by marine ice sheet instability, with their asynchronous onsets of deglaciation derived from their diachronous response times to the southwestward migration of the grounding-line retreat until their synchronous termination of deglaciation at ∼6 ka. A post-LGM deglaciation model with the southwestward migration of the western Ross Ice Shelf grounding line provides the best match to the terrestrial exposure dating results of the thinning patterns of the outlet glaciers along the Victoria Land coast. • Priestley Glacier lowered by ∼254 m on Inexpressible Island during the mid-Holocene (8.9–5.9 ka). • Priestley Glacier lowered faster than the northern Victoria Land glaciers, but slower than the southern Victoria Land ones. • Glacier retreat began asynchronously along the Victoria Land coast, migrating in a southwesterly direction. • The end of deglaciation and sea-level rise, and starting of isostatic rebound and relative sea level fall occurred ∼6 ka. • Glacier retreat was caused by marine ice sheet instability, amplified by complex deglaciation triggers. [ABSTRACT FROM AUTHOR]

The outer Ross Sea continental shelf has experienced large variations in ice sheet extent over the Pleistocene that are theorized to be largely driven by changes in the westward-flowing Antarctic Slope Current (ASC) at the continental shelf break. This current regulates southward incursions of warm modified Circumpolar Water, and it is thought to have triggered past marine ice sheet retreat. Additionally, expansions of grounded ice sheets on the continental shelf have fundamentally altered the Ross Sea water mass formation processes, influencing surface water salinity, sea ice cover, nutrient utilization, deep-water ventilation, and primary productivity. Here, we report the geochemical, physical properties, grain size, bulk δ15N, and diatom records during the late Pleistocene from two sediment cores from the Iselin Bank on the outermost continental shelf in the Ross Sea. These core sites were not overridden by grounded ice sheets during the late Pleistocene glacial-interglacial cycles, allowing for a continuous archive of glacimarine environments that were influenced by the ASC. Interglacial periods are typically characterized by high surface water productivity and nutrient utilization, with Chaetoceros resting spores indicating nutrient limitation under open ocean conditions, and glacial periods are typically characterized by low surface water productivity and nutrient utilization, with sea ice diatoms and planktonic foraminifers indicating light limitation under extensive sea ice/ice margin proximal conditions. A grain size analysis indicates coarse-skewed distributions and winnowing in the Iselin Bank region during cold periods. The winnowing may be related to enhanced ASC flow instead of density driven shelf water outflow. [ABSTRACT FROM AUTHOR]

The Jangbogo Hills are erratic-covered landforms consisting of a series of benches that are parallel to the length of Campbell Glacier, northern Victoria Land, Antarctica. We sampled 41 erratic cobbles from six benches to reveal the exposure times of glacier erratics using in situ 10Be and 26Al. The erratics from the upper three benches yield exposure ages older than Marine Isotope Stage (MIS) 4, with most exposed since MIS 5. However, the lower three benches exhibit tight clusters of exposure ages that range from MIS 3 to the Holocene. Campbell Glacier underwent rapid downwasting during MIS 5, centered at 98.3 ka from its maximum position at the penultimate glacial maximum (PGM). This downwasting continued throughout the last glacial period, with a potential minor stagnation around a bench (∼90 m asl) between 35.4 and 17.0 ka. Our cosmogenic nuclides surface exposure dating results highlight three important points concerning the glacial history of Terra Nova Bay since the penultimate glacial maximum (PGM) in northern Victoria Land, Antarctica: 1) Campbell Glacier was thicker at the PGM than at the global last glacial maximum (LGM); 2) the local LGM occurred during MIS 4; and 3) the extent of Campbell Glacier during the global LGM (90 m) was much smaller than previously assumed (300–400 m). Hence, the previous view that the local LGM (MIS 4) in Victoria Land, Antarctica was synchronous with the global LGM (MIS 2) should be treated with caution. • >500 m lower ice surface in Terra Nova Bay at the last glacial maximum compared with the penultimate glacial maximum. • Local LGM occurred at MIS 4 or 3, before 37 ka. • Campbell Glacier has undergone downwasting since MIS 3, with a possible minor MIS 2 stagnation. • Glacier expansion was stagnated during the global last glacial maximum which is consistent with other areas in Victoria Land. • Campbell Glacier has thinned by > 300 m since MIS 5. [ABSTRACT FROM AUTHOR]

Meltwater history of the Antarctic bivalve Laternula elliptica in Maxwell Bay, King George Island near the Antarctic Peninsula was reconstructed during the shell growth. High resolution trace elemental and stable isotopic compositions along the aragonite outer part of the shell together with growth bands shows that the shell lived for 9 years with distinct annual cycles. Also oxygen and carbon isotope values reveal the local meltwater history in Antarctic Peninsula region. More negative oxygen isotope values than the predicted equilibrium values clearly show that oxygen isotope depletion is due to lower salinity of seawater by glacial melting. This is also confirmed by the similar trend of low carbon isotope values as well as monitored sea surface salinity values. Comparing δ18O values of previous results using the same bivalve species, more negative values from the Antarctic Peninsula (Maxwell Bay) during the austral winter than from East Antarctica (Syowa Coast and Ross Sea) suggests that perennial glacial melting influenced seawater δ18O composition near the peninsula. Also, more negative and variable bivalve δ18O values during austral summer indicate that meltwater pulses fluctuated greatly in the study area. Distinctively different trends in bivalve δ18O profiles between the Antarctic Peninsula and East Antarctica may reflect differential responses to regional warming with regard to the recent global warming over the past few decades. • Age determination of the bivalve shell using Mg and Sr variations • Construction of meltwater input history using stable isotopes of the bivalve shell • Comparison of meltwater histories between Antarctic Peninsula and East Antarctica • Relationship of glacial melting pulses to atmospheric circulation with global warming [ABSTRACT FROM AUTHOR]