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Cross-equatorial ocean heat transport (OHT) changes have been found to damp meridional shifts of the intertropical convergence zone (ITCZ) induced by hemispheric asymmetries in radiative forcing. Zonal-mean energy transport theories and idealized model simulations have suggested that these OHT changes occur primarily due to wind-driven changes in the Indo-Pacific’s shallow subtropical cells (STCs) and buoyancy-driven changes in the deep Atlantic meridional overturning circulation (AMOC). In this study we explore the partitioning between buoyancy and momentum forcing in the ocean’s response. We adjust the top-of-atmosphere solar forcing to cool the Northern Hemisphere (NH) extratropics in a novel set of comprehensive climate model simulations designed to isolate buoyancy-forced and momentum-forced changes. In this case of NH high-latitude forcing, we confirm that buoyancy-driven changes in the AMOC dominate in the Atlantic. However, in contrast with prior expectations, buoyancy-driven changes in the STCs are the primary driver of the heat transport changes in the Indo-Pacific. We find that buoyancy-forced Indo-Pacific STC changes transport nearly 4 times the amount of heat across the equator as the shallower wind-driven STC changes. This buoyancy-forced STC response arises from extratropical density perturbations that are amplified by the low cloud feedback and communicated to the tropics by the ventilated thermocline. While the ocean’s specific response is dependent on the forcing scheme, our results suggest that partitioning the ocean’s total response to energy perturbations into buoyancy and momentum forcing provides basin-specific insight into key aspects of how the ocean damps ITCZ migrations that previous zonal-mean frameworks omit.

As a crucial part of the Asian monsoon stretching from tropical India to temperate East Asia, the Indian monsoon (IM) contributes predominant precipitation over Asian continent. However, our understanding of IM’s onset, development and the underlying driving mechanisms is limited. Increasing evidence indicates that the IM began in the Eocene or even the Paleocene and was unexceptionally linked to the early rise of the Tibetan Plateau (TP). These were challenged by the heterogeneous and diachronous uplift of the TP and all the reported records were confined to tropical zone under tropical monsoon driven by the Intertropical Convergence Zone (ITCZ) that is irrelevant to the TP. Therefore, reliable paleoclimatic records from the extra-tropical IM region is crucial to reveal how the tropical IM expanded to subtropical and temperate zones and what driving factors might be related to it. Here we present robust Eocene paleoenvironmental records from central Yunnan (~26°N) in subtropical East Asia. The multiproxy results of two sites demonstrate a consistent sudden switch from a dry environment in the early Eocene to a seasonally wet one at 41 Ma, suggesting a jump of the tropical IM to the southern subtropical zone at 41 Ma. The full collision of India with Asia, and the resulting changes in paleogeography at 41 Ma (closure of the Neotethys sea, retreat of the Paratethys seas, fast northward movement of the southern margin of the TP and rise of the central TP), aided by synchronous Antarctic cooling, might have worked together to drive the IM enhancement and northward expansion.

The global monsoon (GM) comprises two major modes, namely, the solstitial mode and equinoctial asymmetric mode. In this paper, we extend the GM domain from the tropics to the global region and name it the global spring—autumn monsoon (GSAM), which mainly indicates a spring—autumn asymmetrical precipitation pattern exhibiting annual variation. Its distribution and possible formation mechanisms are also analyzed. The GSAM domain is mainly distributed over oceans, located both in the midlatitude and tropical regions of the Pacific and Atlantic. In the GSAM domains of both the Northern and Southern Hemispheres, more precipitation occurs in local autumn than in local spring. The formation mechanisms of GSAM precipitation vary according to the different domains. GSAM precipitation in the tropical domain of the Eastern Hemisphere is influenced by the circulation differences between the onset and retreat periods of the Asian summer monsoon, while tropical cyclone activities cause precipitation over the South China Sea (SCS) and western North Pacific (WNP). GSAM precipitation in the tropical domain of the Western Hemisphere is influenced by the tropical asymmetrical circulation between the Northern and Southern Hemispheres and the variation in the intertropical convergence zone (ITCZ) driven by the intensity of the sea surface temperature cold tongues over the equatorial eastern Pacific and eastern Atlantic. GSAM precipitation in the midlatitude domain is influenced by the differences in water vapor transportation and convergence between spring and autumn. In addition, GSAM precipitation is also affected by extratropical cyclone activities.

Changes in land surface albedo and land surface evaporation modulate the atmospheric energy budget by changing temperatures, water vapor, clouds, snow and ice cover, and the partitioning of surface energy fluxes. Here idealized perturbations to land surface properties are imposed in a global model to understand how such forcings drive shifts in zonal mean atmospheric energy transport and zonal mean tropical precipitation. For a uniform decrease in global land albedo, the albedo forcing and a positive water vapor feedback contribute roughly equally to increased energy absorption at the top of the atmosphere (TOA), while radiative changes due to the temperature and cloud cover response provide a negative feedback and energy loss at TOA. Decreasing land albedo causes a northwards shift in the zonal mean intertropical convergence zone (ITCZ). The combined effects on ITCZ location of all atmospheric feedbacks roughly cancel for the albedo forcing; the total ITCZ shift is comparable to that predicted for the albedo forcing alone. For an imposed increase in evaporative resistance that reduces land evaporation, low cloud cover decreases in the northern mid-latitudes and more energy is absorbed at TOA there; longwave loss due to warming provides a negative feedback on the TOA energy balance and ITCZ shift. Imposed changes in land albedo and evaporative resistance modulate fundamentally different aspects of the surface energy budget. However, the pattern of TOA radiation changes due to the water vapor and air temperature responses are highly correlated for these two forcings because both forcings lead to near-surface warming.

Sedimentological, geochemical, and paleontological investigations of the coastline of northeastern Oman have provided the authors with an in-depth insight into Holocene sea levels and climate conditions. The spatial distribution and species assemblage of mangrove ecosystems are analyzed. These ecosystems are sensitive to changes in sea level and precipitation and thus reflect ecological conditions. The close proximity to archaeological sites allows us to draw conclusions regarding human interaction with the mangrove ecosystems. Our interdisciplinary inquiry reveals that the mangrove ecosystems along the east coast of Oman collapsed ~6000 cal yr BP on a decadal scale. There is no sedimentological evidence for a mid-Holocene sea-level highstand. The ecosystem collapse was not caused by sea-level variation or anthropogenic interferences; rather, it was the consequence of reduced precipitation values related to a southward shift of the Intertropical Convergence Zone. This resulted in a decrease of freshwater input and an increase in soil salinity. Further, the aridification of the area caused increased deflation and silting up of the lagoons.

Author(s): Huang, Huilin; Xue, Yongkang; Chilukoti, Nagaraju; Liu, Ye; Chen, Gang; Diallo, Ismaila | Abstract: AbstractLand-use and land-cover change (LULCC) is one of the most important forcings affecting climate in the past century. This study evaluates the global and regional LULCC impacts in 1950–2015 by employing an annually updated LULCC map in a coupled land–atmosphere–ocean model. The difference between LULCC and control experiments shows an overall land surface temperature (LST) increase by 0.48 K in the LULCC regions and a widespread LST decrease by 0.18 K outside the LULCC regions. A decomposed temperature metric (DTM) is applied to quantify the relative contribution of surface processes to temperature changes. Furthermore, while precipitation in the LULCC areas is reduced in agreement with declined evaporation, LULCC causes a southward displacement of the intertropical convergence zone (ITCZ) with a narrowing by 0.5°, leading to a tripole anomalous precipitation pattern over the warm pool. The DTM shows that the temperature response in LULCC regions results from the competing effect between increased albedo (cooling) and reduced evaporation (warming). The reduced evaporation indicates less atmospheric latent heat release in convective processes and thus a drier and cooler troposphere, resulting in a reduction in surface cooling outside the LULCC regions. The southward shift of the ITCZ implies a northward cross-equatorial energy transport anomaly in response to reduced latent/sensible heat of the atmosphere in the Northern Hemisphere, where LULCC is more intensive. Tropospheric cooling results in the equatorward shift of the upper-tropospheric westerly jet in both hemispheres, which, in turn, leads to an equatorward narrowing of the Hadley circulation and ITCZ.

Whether the Indian Summer Monsoon (ISM) Maximum started in the early Holocene or middle Holocene remains a controversial issue. Grain-size measurements were conducted on 157-cm-long core ADM-C1 from the Andaman Sea; the core spanned the last 11.2 kyr BP. Four end-members (EMs) were unmixed using lognormal parametric end-member modeling. Genetic analyses of the grain-size EMs suggested the EM1 and EM2 may correlate with suspension in the upper layers and transportation in the benthic nepheloid layer, respectively, while the EM3 and EM4 were tied with deposition affected by monsoonal currents and sedimentation under extreme events, respectively. The EM3 was dominated by ISM intensity and transported by summer monsoon currents, with increase in the proportion of EM3 reflecting increasing ISM intensity, and vice versa. Variations in EM3 were used to define three stages of ISM evolution, as follows: (1) During 11.2–9.1 kyr BP, EM3 was relatively low, indicating a weak ISM; (2) during 9.1–4.5 kyr BP, EM3 increased substantially, indicating a strengthened ISM; (3) during 4.5-0 kyr BP, EM3 decreased gradually, suggesting a gradual weakening of the ISM. The Holocene ISM Maximum started at ~9.1 kyr BP rather than in the early Holocene, which may have been partly due to the slowdown of the Atlantic meridional overturning circulation (AMOC) during the early Holocene that resulted in a decreased land-sea thermal contrast between the landmass and the Indian Ocean. An additional cause may have been the remnant Northern Hemisphere ice sheets that impeded the northward shift of the Intertropical Convergence Zone (ITCZ). Seven relatively brief decreases in the ISM intensity (events 7, 6, 5, 4, 3, 2, 1) occurred at ca. 10.3, 9.7, 7.3, 5.7, 4.2, 2.4, and 0.8 kyr BP, respectively. They corresponded, within the age uncertainties, to the increased supplies of ice-rafted detritus to North Atlantic sediments, implying that changes in the ISM intensity on millennial scale were dominated by climatic processes in northern high latitudes.

The global atmospheric water transport from the evaporation to the precipitation regions has been traced using Lagrangian trajectories. A matrix has been constructed by selecting various group of trajectories based on their surface starting(evaporation) and ending (precipitation) positions to show the connectivity of the atmospheric water transport within and between the three major ocean basins and the global landmass. The analysis reveals that a major portion of the evaporated water precipitates back into the same region, namely 67 % for the Indian, 64 % for the Atlantic, 85 % for the Pacific Ocean and 72 % for the global landmass. The evaporation from the subtropical regions of the Indian, Atlantic and Pacific Oceans is found to be the primary source of atmospheric water for precipitation over the Intertropical Convergence Zone (ITCZ) in the corresponding basins. The evaporated waters from the subtropical and western Indian Ocean were traced as the source for precipitation over the South Asian and Eastern African landmass, while Atlantic Ocean waters are responsible for rainfall over North Asia and Western Africa. Atlantic storm tracks were identified as the carrier of atmospheric water that precipitates over Europe, while the Pacific storm tracks were responsible for North American, eastern Asian and Australian precipitation. The bulk of South and Central American precipitation is found to have its source in the tropical Atlantic Ocean. The recycling of evapotranspirated water from land is pronounced over the western coast of South America, Northeastern Asia, Canada and Greenland. The ocean-to-land and land-to-ocean water transport through the atmosphere was computed to be 2 × 109 kg/s and 1 × 109 kg/s, respectively. The difference between them (net ocean-to-land transport), i.e. 1 × 109 kg/s, is transported to land. This net transport is approximately the same as found in previous Eulerian estimates.

The southern coast of Hainan Island, China, is one of the most frequently hit areas of tropical cyclones in the Northwest Pacific regions. Although some of the extreme typhoon events were known in historical times, quantitative information on the timing and magnitude of paleo-typhoon events in this coastal area remains rare. In the present study, a large number of coral reef boulders were found on the Xiaodonghai reef platform, on the south coast of Hainan Island. Morphometric analysis of the boulders shows an exponentially fining landward trend, indicating a storm origin; a wave-induced current velocity of 2.41–5.71 m/s during the storm events is required to transport the boulders that were originally situated outside the reef edge. Based on the U/Th and 14C dating for the age-indicating samples taken from the boulders, seven major periods with intense typhoon activities were identified for the last 4,000 years, i.e., 1800–1500 BCE, 1200–900 BCE, 50–120 CE, 550–800 CE, 900–1000 CE, 1350–1900 CE, and 1910–2000 CE. A comparison with the regional typhoon records in terms of climatic parameters in the northwestern Pacific and the South China Sea regions indicates that the longitudinal variations of intense typhoon frequency were mainly controlled by El Niño-Southern Oscillation (ENSO), dominantly modulated by the Intertropical Convergence Zone. Because of the future warming climate, there will be a trend of enhanced typhoon risk for the southern Hainan Island coasts.

In the zonal direction, the downward branch of the Walker circulation above the Indian Ocean is only 20 degrees thick, whereas the Pacific counterpart is 90 degrees thick. This zonal sharpness is r...

The North Pacific Subtropical Gyre circulation redistributes heat from the Western Pacific Warm Pool towards the mid- to high-latitude North Pacific. However, the driving mechanisms of this circulation and how it changed over the Holocene remain poorly understood. Here, we present alkenone-based sea surface temperature reconstructions along the Kuroshio, California and Alaska currents that cover the past ~7,000 years. These and other paleorecords collectively demonstrate a coherent intensification of the boundary currents, and thereby the basin-scale subtropical gyre circulation, since ~3,000–4,000 years ago. Such enhanced circulation during the late Holocene appears to have resulted from a long-term southward migration of the Intertropical Convergence Zone, associated with Holocene ocean cooling. Our results imply that the North Pacific Subtropical Gyre circulation could be weakened under future global warming., Long-term variability of the North Pacific Subtropical Gyre (NPSG) circulation is not well understood. Here, the authors present data from different boundary currents that shows an enhanced NPSG circulation since ~3000-4000 years ago, linked to a southward migration of the Intertropical Convergence Zone.

Within the context of anthropogenic warming, rainfall oscillations may induce especially important societal impacts worldwide. In this article, we propose to study potential underlying mechanisms related to precipitation changes on a planetary scale by taking advantage of the recent theory of Rossby waves of long periods winding around subtropical gyres, the Gyral Rossby Waves (GRWs). The stable oxygen isotopic compositions of speleothems are used to regionalize and reconstruct the evolution of long-term rainfall oscillation during the Holocene. The method applied here consists in estimating the wavelet power of dated series of stable oxygen isotopic composition (δ18O) in speleothems within period bands representative of subharmonic modes. Our findings highlight: (1) hydrological processes resulting from friction between the North Equatorial Current (NEC) and the North Equatorial Counter Current (NECC) to explain the weakening of ENSO activity in mid-Holocene, and (2) the quasi-resonance of the equatorward migration of the summer Inter Tropical Convergence Zone (ITCZ) during the Holocene, because of the progressive decrease of the thermal gradient between the low and high latitudes of the gyres. The results of this study suggest that the spatial and temporal variations in the amplitude of the rainfall oscillations are related both on the acceleration/deceleration phases of the western boundary currents and on the shrinkage of the Hadley cell. The latitudinal shift of the summer ITCZ in response to changes in the thermal gradient is of the utmost importance in predicting the expansion of deserts resulting from anthropogenic warming.

The meridional migration of the bifurcation latitude of the Pacific North Equatorial Current (NEC) in the western boundary of the tropical Pacific modulates the strength of the Kuroshio Current. Using salinity reanalysis data, we show the NEC bifurcation latitude also acts as the dominant control on thermocline salinity of the Sulu Sea, just west of the Philippine archipelago, by regulating influx of western Pacific thermocline water via the Luzon Strait. We used oxygen isotopes (δ18O) and Mg/Ca in the thermocline-dwelling foraminifera Globorotalia tumida from Sulu Sea sediment core MD97-2141 to determine past thermocline δ18Ow and salinity variability spanning ∼20–5 ka with an average sampling interval of ∼50 years and infer past changes in the NEC bifurcation latitude. Our Sulu Sea thermocline reconstruction reveals high salinity from ∼18.8–15.5 ka, ∼12.2–11.5 ka, and from ∼9.5–8.5 ka indicating the NEC bifurcation latitude was shifted north and the Kuroshio was weak at those times. Low Sulu Sea thermocline salinity from ∼13.0–12.4 ka, ∼11.5–10.9 ka, and from ∼8.5 ka until the end of the record at ∼5.6 ka indicates the NEC bifurcation latitude was shifted south and the Kuroshio Current was relatively strong. Comparison to other paleoclimate records suggests the observed northward (southward) shifts of the NEC bifurcation latitude were driven by southward (northward) shifts of the Indo-Pacific ITCZ, consistent with modern mechanisms controlling interannual NEC bifurcation variability. The NEC bifurcation latitude shifts likely modulated northward energy transport via the Kuroshio Current and the mean temperature and salinity of the Indonesian Throughflow.

During African Humid Period in the Holocene when the summer Intertropical Convergence Zone migrated to its northernmost position, the Qarun Lake in the Faiyum Oasis in Egypt was fed with regular inflows from the Nile River and rainfall brought by the Mediterranean winter circulation. Finely-laminated lake sediments, dated at 8.5–6.7 cal kyr B.P., were examined in terms of lithology, geochemistry, microfossils (diatom, pollen) and magnetic susceptibility. Based on the inferred geographical derivation of pollen, the environmental affiliation of diatom taxa and geochemistry of lake sediments, wind trajectories were distinguished, related to two main atmospheric circulation phases. During the earlier phase (8.50–7.83 cal kyr B.P.) there were northwestern wind trajectories followed by southern ones and during the later phase (7.83–6.70 cal kyr B.P.), the northern winds were followed by northwestern and southern ones. Northwestern and northern winds brought winter rainfall and caused water turbulence in the lake, and the southern winds were associated with regional aridification. This scenario of atmospheric circulation in northeastern Africa extends significantly our understanding of key modes of climatic variability and wind trajectories in the Early to Middle Holocene (Greenlandian to Northgrippian) transition.

Identifying variability and the mechanisms driving variability in the Indian summer monsoon (ISM) since the last deglaciation is critical for understanding past hydroclimatic change. In this study, we present an accelerator mass spectrometry radiocarbon dated record of delta O-18 variations in authigenic carbonates derived from Lake Chenghai in southwest China, a region that receives moisture mainly from the Indian Ocean. The delta O-18 values vary from -11.9 to +0.1 parts per thousand, providing a detailed record of variations in ISM precipitation delta O-18 values, and lake hydrological balance. The record shows that the ISM generally strengthened in the post-glacial between 15.6 and 8.8 cal ka BP, but that three centennial to millennial-scale drought events were superimposed on the long-term trend. Drought events, as indicated by substantial positive shifts in 8 18 0 value, occurred from 15.6 +/- 0.2 to 14.4 +/- 0.2, 12.5 +/- 0.2 to 11.7 +/- 0.2 and 10.1 +/- 0.1 to 10.0 +/- 0.1 cal ka BP, corresponding to the Heinrich 1, Younger Dryas, and Bond 7 cold events in the North Atlantic region, respectively. The timings of these droughts are suggested to be related to meltwater discharge into the North Atlantic. The weakened Atlantic Meridional Overturning circulation, which leads in turn to the southward migration of the intertropical convergence zone and cooling in the tropical Indian Ocean.

The 2015/2016 El Nino event reached the threshold of super El Nino event, and was comparable to the super events in 1982/1983 and 1997/1998. Interestingly, the tropical cyclones (TCs) were found to have very late onsets in the decaying years of the super El Nino events. This study discusses the causes of late TC onsets related with atmospheric circulation, disturbance sources and trigger mechanisms. The analysis shows that the western North Pacific subtropical high (WNPSH) from January-June during the decaying years of the super El Nino events were stronger than the climatic mean, which resulted in a relatively stable atmospheric state by inhibiting deep convection. As a disturbance source, the April-June intertropical convergence zone (ITCZ) during the decaying years of the super El Nino events were significantly weaker than its climatic mean. The cross-equatorial flow and monsoon trough, as important TC generation triggers, were weaker from April-June during the decaying years of the super El Nino events, which further reduced the probability of TC generation. As for the late TC onsets, the role of atmospheric circulation anomalies (i.e., subtropical-high, the ITCZ, cross-equatorial flow, and monsoon trough) were more important. The cross-equatorial flow may take as predictor of TC onsets in the decaying years of the super El Nino events.

Spectral analysis of sediment from International Ocean Discovery Program (IODP) Site U1433 in the South China Sea can be used to constrain humidity and temperature through time by constructing hematite/goethite records spanning the last 10 million years. Records in the southwest and northern parts of this basin show long-term contrasting trends, despite the fact that geochemical evidence for alteration is similar in both parts of the basin, i.e. towards less alteration since 10 Ma. However, contrasting clay mineral assemblages in the northern and southwestern areas do suggest long-term changes in the relative climate of Indochina and southern China. We interpret this to reflect the northward migration of the ITCZ since the Miocene resulting in a progressive drying of Indochina and increasingly wet conditions in South China. Sediment believed to be supplied from the Mekong River (IODP Site U1433) shows increasing chemical weathering at a time of long-term drying of the climate. This probably reflects increasing chemical weathering driven by slower transport and despite reduced rates of chemical alteration in the context of a colder, drier climate since the Miocene. In general hematite/goethite data are consistent with pollen constraints from the same drill site that show colder conditions with increasing hematite/goethite since 3 Ma and with a transition to apparently wetter conditions since the mid-Pleistocene transition (MPT). This implies that most of the sediment in the southwestern basin is weathered and eroded during warmer, wetter interglacial phases, at least since the MPT.

The tropical Eastern Pacific Fresh Pool (EPFP) has some of the highest precipitation rates and lowest sea surface salinities found in the open ocean. In addition, the sea surface salinity in the EPFP exhibits one of the strongest annual cycles in the world ocean. The region is strongly affected by the meridionally migrating Intertropical Convergence Zone and is also influenced by large-scale ocean currents and wind-driven Ekman currents. Recognizing the complexity of competing regional influences and the importance of sea surface salinity as an integrator of freshwater forcing, the Salinity Processes Upper-ocean Regional Study (SPURS) was undertaken to better understand how ocean processes and surface freshwater fluxes set surface salinity. Instrumentation on a surface mooring, deployed for 14 months near the western edge of the EPFP, allowed estimation of the surface fluxes of momentum, heat, and freshwater. Subsurface instrumentation on the mooring provided upper-ocean vertical structure and horizontal currents. These observations, along with horizontal gradients of surface salinity from the Soil Moisture Active Passive (SMAP) satellite instrument, were used to estimate the surface-layer salinity budget at the western edge of the EPFP. While the low salinity associated with the presence of the EPFP at the mooring site was sustained by heavy rainfall, it was found that seasonal variability in large-scale currents was important to controlling the transition between the “salty” and “fresh” seasons. Ekman advection was important to prolonging local high salinity as rainfall decreased. Although illuminating some key processes, the temporal variability of the surface-layer salinity budget also shows significant complexity, with processes such as surface freshwater fluxes and vertical mixing making notable contributions. The surface flux term and the terms involving mixing across the base of the surface layer oppose and nearly cancel each other throughout the deployment, such that the horizontal advection term effectively accounts for most of the variability in surface salinity at the site on monthly to seasonal timescales. Further investigation, taking advantage of additional observations during SPURS-2, will be needed to more thoroughly examine the relevant physical processes.

We present the annual cycles of the monthly surface and advective heat fluxes from La Boquilla and Tangolunda, two points in the western margin of the Gulf of Tehuantepec. Computations are function of averaged (2011–2013) daily seawater temperature at 5 m depth, interpolated daily SST satellite and daily meteorological data except cloud cover, estimated from ICOADS. The advective heat flux is a result of the imbalance between the net surface heat flux and the heat content rate of change in a 25 m depth water column. Most of the meteorological variables and heat fluxes, show intra-seasonal variability related to the cloud cover that accompanies the Intertropical Convergence Zone position relative to the study area. The latent heat flux, calculated using two distinct exchange coefficients, according to Bunker and to Liu, and the long wave heat flux, are about the same magnitude in each site. In all the computations, the net surface heat flux is positive throughout the year (into the ocean) and correspondingly there is an exportation of advective heat flux along the year from the water column. Large advective heat losses, in February and October, occur when measured southeastward currents are strong. Small losses occur, in May and January, when currents are weak and towards different directions. Currents arriving to the area from the west, seem correspond to mixed water from the tropical Pacific off central Mexico in February. In October, however, similar currents seem to be part of the Costa Rica Coastal Current after leaving the Tehuantepec Bowl. The largest net surface heat flux difference between the two sites (

Atmospheric CO2 concentrations (pCO2) varied on millennial timescales in phase with Antarctic temperature during the last glacial period. A prevailing view has been that carbon release and uptake by the Southern Ocean dominated this millennial‐scale variability in pCO2. Here, using Earth System Model experiments with an improved parameterization of ocean vertical mixing, we find a major role for terrestrial and oceanic carbon releases in driving the pCO2 trend. In our simulations, a change in Northern Hemisphere insolation weakens the Atlantic Meridional Overturning Circulation (AMOC) leading to increasing pCO2 and Antarctic temperatures. The simulated rise in pCO2 is caused in equal parts by increased CO2 outgassing from the global ocean due to a reduced biological activity and changed ventilation rates, and terrestrial carbon release as a response to southward migration of the Intertropical Convergence Zone. The simulated terrestrial release of carbon could explain stadial declines in organic carbon reservoirs observed in recent ice core δ13C measurements. Our results show that parallel variations in Antarctic temperature and pCO2 do not necessitate that the Southern Ocean dominates carbon exchange; instead, changes in carbon flux from the global ocean and land carbon reservoirs can explain the observed pCO2 (and δ13C) changes.

The initiation of Asian monsoon systems is a complex and controversial issue, and the existence of monsoon systems in the Eocene has not yet been confirmed by commonly applicable proxy data. Eocene palynological records from three basins in southern China provide an ideal opportunity to investigate the early stage of the Asian monsoon due to their unique geographical location. The palynological assemblages suggest that the middle Eocene vegetation in southern China was composed of mixed evergreen and deciduous broad-leaved forests, accompanied by abundant subtropical to tropical evergreen taxa, thus bearing strong resemblance to the modern vegetation in southern China, and indicating a warm-humid subtropical climate. By analysing the palynological data using a coexistence approach (CA), we quantitatively reconstructed seven climatic parameters, which indicate a subtropical monsoon climate with a mean annual temperature (MAT) in the range 16.5 to 23.5 °C and a mean annual precipitation (MAP) in the range 1035 to 1724 mm, similar to those of the modern subtropical monsoon climate in southern China although the MAT was surprisingly lower than present. Significant seasonal variations in precipitation and temperature and as well as the spatial distribution of MAP during the middle Eocene were most similar to those of the modern East Asia Monsoon (EAM) climate of southern China, clearly indicating that the Eocene climate of southern China was mainly influenced by the EAM, rather than the Indian monsoon (IM) or Inter-tropical Convergence Zone (ITCZ) monsoons. By combining the above results with previously published geological evidence, we infer that the EAM developed in southern China as early as the middle Eocene, albeit with an intensity that may have been weaker than present. The establishment of the middle Eocene EAM in southern China was most likely driven by the northward drift of the Indian Subcontinent and its collision with the Eurasian continent, associated with the uplift of the Central-Southern Tibetan Plateau, which enlarged the land-sea thermal contrast and deepened the low pressure over continental Asia in summer, thus greatly intensifying the East Asian subtropical summer monsoon over southern China.

Two sediment cores collected in the shelf off Rio de Janeiro (RJ13-01B: 10.8 cal kyr BP, and RJ13-02B: 4.7 cal kyr BP) were investigated in high-resolution to evaluate changes in sedimentary processes and paleoclimatic and paleoceanographic variability during the Holocene in the Southeastern Brazil. Information from inorganic proxies of continental input (Al/Ca and Fe/Ca), redox-sensitive elements (Fe/Al, V/Al and Mn/Al), paleoproductivity (Sr/Al, Cd/Al and Ba/Al), as well as data for grain size, geophysical properties (p-wave velocity, gamma-ray density, acoustic impedance, magnetic susceptibility and porosity), Si, total organic carbon and calcium carbonate were considered. The data revealed three main periods of sediment accumulation: (i) from 10.8 cal kyr BP to 7.6 cal kyr BP the sediment was coarse, Si content was high (27%), the magnetic susceptibility was low and the presence of shell fragments all suggest a period of low continental input and the deposition site was shallow (i.e, lower sea level); (ii) from 7.5 cal kyr BP to 4.6 cal kyr BP the elevated ratios of Al/Ca (0.69 ± 0.08), Fe/Ca (0.27 ± 0.04), Sr/Al (31.57 ± 4.47) ×10−4, Cd/Al (0.09 ± 0.03) ×10−5 and Ba/Al (0.70 ± 0.16) ×10−4 are consistent with a period of maximum sea transgression and elevated influence of the nutrient-rich South Atlantic Central Water (SACW); (iii) from 4.5 cal kyr BP to the present, events of higher fluxes of TOC, Ni, Cu and Zn were observed from ca 3.2 cal kyr BP to 3.4 cal kyr BP, in both cores, related to humid climate. Overall, the multi-proxy approach shed light on the effects of climate and oceanographic variability on sediment input and accumulation in a less-studied portion of the Brazilian shelf, which are consistent with other shelf areas and with changes in regional climate systems like the Intertropical Convergence Zone (ITCZ), South American Monsoon Systems (SAMS) and South Atlantic Convergence Zone (SACZ).

We present a sub-centennial resolution summer temperature record from the SE Tibetan Plateau (Tiancai Lake, SW China, 3900 m a.s.l.) derived from a chironomid stratigraphy covering the last c.19.5 ka. The record highlights the interaction between tropical and high-latitude climate forcing through the changes in atmospheric circulation during the last deglaciation. The scale of the last glacial maximum (LGM) cooling is consistent with other tropical mountain regions at c.5 °C and a rapid recovery of temperatures at 19.0 ka is related to changes in adiabatic lapse rates at the end of the glaciation. The overall pattern of change shows that North Atlantic deglaciation climate events (the Heinrich 1 and Younger Dryas cooling events and the Bolling–Allerod warm period) are all recorded, but the influence of the events decline as the deglaciation progresses. We relate these patterns to North Atlantic Deep water ventilating the Southern Ocean and to the consequent movements of the Intertropical Convergence Zone (ITCZ) in the Indian Ocean Basin as transmitted through changes in the southern mid-latitude circulation.

The South China Sea (SCS) is an important moisture and heat source in the Asian monsoon system, and its environmental changes influence economic and social stability in Southeast Asia and East Asian. Previous records on sea surface temperature (SST) and salinity (SSS) were mostly from one sediment core, and/or only showed fragmentary information. It is hard to provide insights into the mechanisms of the overall paleoceanographical environmental variability in the northern SCS. In this study, paired δ18O and Mg/Ca records of planktonic foraminifer Globigerinoides ruber from Core S0204B nearby the Luzon Strait (21°13.818′N, 118°3.077′, water depth 1822 m), and Core GHE 27L (19.85°N, 115.34°E, water depth of 1533 m) in the central northern SCS, were analyzed, so as to better understand the physical process of the SST and SSS changes in the northern SCS and its relationship with the tropical Pacific. The results demonstrate that the SST is relatively stable and seawater δ18O (δ18Osw) values, a salinity proxy, shows a decrease trend since 7.0 ka BP in Core S0204B. By contrast, SST and δ18Osw in Core GHE 27L exhibit an overall increasing trend at the same time, indicating apparent regional discrepancy on the changing trend of the SST and SSS in the northern SCS. We suggest that the thermal and hydrographic conditions in Core S0204B were primarily influenced by the outer western Pacific water. However, the thermal and hydrographic conditions in Core GHE 27L may be predominantly controlled by the weakened Asian monsoon during the mid-late Holocene, which was induced by the southern migration of Intertropical Convergence Zone (ITCZ) and stronger EI Nino Southern Oscillation.

The variation of stable isotopes between individual shells of planktic foraminifera of a given species and size may provide short-term seasonal insight into past sea surface temperature (SST) and salinity (SSS). In this context, oxygen isotope analyses of individual Globigerinoides sacculifer were carried out from the Ocean Drilling Program Site 723A in the western Arabian Sea to unravel seasonal changes over the last 22 kyr. δ18O values of single shells of G. sacculifer range from of 0.54–2.09‰ at various discrete depths in the core which spans the last 22 kyr. Maximum inter-shell δ18O variability and relatively higher standard deviation is noticed from 20 to 10 kyr (deglaciation), whereas from 10 kyr onwards (Holocene) inter-shell δ18O variability decreases. Based on statistical inferences, we interpret this result as greater seasonal SST and SSS contrasts during the deglaciation compared to the Holocene. These winter-to-summer contrasts during the deglaciation can likely be explained by a net reduction in summer upwelling linked to changes in wind forcing and net evaporation-minus-precipitation that might, along with local causes, be related to deglacial shifts in the intertropical convergence zone (ITCZ). We note that a common winter-dominated SST signal in the Arabian Sea and in Greenland was pervasive during the last glacial period, strengthening evidence of a North Atlantic link with Indian Ocean SST. Thus, the present study has wider implications in understanding whether the forcing mechanism of tropical monsoon climate lies in high latitudes or in the tropics.

Variability in surface currents is mainly induced by the time-varying wind forcing. Recent studies have revealed robust pronounced changes in the atmospheric circulation over the Pacific came with the Pacific Decadal Oscillation (PDO). However, the PDO is a climate index based on sea surface temperature (SST) variations, and may not be appropriately considered as a climate forcing. Here, we suggest the Atlantic SST variability is the ultimate forcing leading to changes in the atmospheric circulation and surface winds over the North Pacific. Anomalous warm North Atlantic and cold South Atlantic leads to weak Hadley cell in the Northern Hemisphere, resulting in a northward displacement of the ITCZ as well as a positive wind stress curl anomaly in the Pacific subtropical region, which would reduce the North Pacific subtropical gyre (NPSG). Associated with reduced sea surface height in the subtropics by the weakened NPSG, the North Equatorial Current (NEC) is weakened based on geostrophy. Changes in basin-scale winds further result in the southward migration of the tropical gyre and consequential downstream ocean circulation.

We study shifts in phytoplankton proxies linked to terrigenous inputs and teleconnections in a core from Soledad Basin, Gulf of Ulloa, NW Mexico, spanning the end of the deglaciation and the Holocene. We used biogenic opal (% opal), organic carbon (% total organic carbon [TOC]), and inorganic carbon (% CaCO3) as proxies of productivity and opal/TOC and CaCO3/TOC ratios as proxies of nutrient uptake and C‐export by siliceous and carbonate organisms. We reconstructed terrestrial inputs and identified authigenic gypsum. Based on opal/TOC and CaCO3/TOC ratios, we found periodic changes of ~0.5, 1.1–1.8 ka cycle in phytoplankton proxies exporting siliceous and carbonate skeletal debris to the sediments. An increase in carbonate organisms occurred during 14–8.7 ka, corresponding to reduced El Niño–Southern Oscillation (ENSO)‐like variability, in parallel to the northward displacement of the Intertropical Convergence Zone (ITCZ) and an overall negative phase of the Pacific Decadal Oscillation (PDO). An increase in siliceous organisms occurred between 6 and 3 ka, coincident with strong ENSO‐like conditions, southern migration of ITCZ, and less intense but more frequent positive PDO‐hydrological variability. Grain size analyses show significant amounts of fine fraction (dust

Earlier studies suggest that the frequency and the strength of ENSO Modoki events increased considerably since last few decades (1970–2010) resulting in a need to revisit the climatic impacts of varying magnitude of ENSO Modoki. Hence, to better understand the impact of ENSO Modoki amplitude over the tropical and extra-tropical regions, especially in the Pacific, Asian and African regions, we conducted ENSO Modoki sensitivity experiments using ICTP-AGCM (SPEEDY). One of the main interests of this study is to see how ICTP-AGCM can reproduce teleconnections induced by ENSO Modoki events and how sensitive is the global and regional climate to ENSO Modoki strength. SPEEDY model qualitatively reproduces the impact of ENSO Modoki over the Pacific, Atlantic, North and South America and African regions very well. However, it underestimates ENSO Modoki-induced teleconnection patterns and associated changes in South Asia, particularly in the Indian region. This study suggests a nonlinear climatic response to increased magnitude of ENSO Modoki. Our results reveal that like conventional ENSO, ENSO Modoki also induces considerable impact over North Pacific (Atlantic) region and initiates strong PNA (NAO) like response. ENSO Modoki-induced negative/positive NAO-like response and associated changes in Southern Europe and North Africa region get significantly strong following increased intensity of El Nino/La Nina Modoki in the boreal winter. We further find that ENSO Modoki magnitude significantly impacts tropical and high latitude circulation cells. The positive phase of ENSO (El Nino) overall strengthens Hadley Cell and a reverse is true for La Nina phase. ENSO Modoki-induced strengthening and weakening of Hadley Cell induce significant impact over South Asian and African ITCZ convective regions through modification of ITCZ/monsoon circulation system.

Highlights • Tobago Basin subsurface temperature and salinity records from ~37 to 30 ka BP. • Cumulative tropical Atlantic upper ocean-atmosphere interactions crucial to functioning of North Brazil Current and Subtropical Gyre. • Rapid re-organizations of the tropical Atlantic upper ocean-atmosphere system at ~32.8 ka BP and ~ 21.8 ka BP. • Thresholds for southward dispersal of Salinity Maximum Water not set during the glacial time period of abrupt climate fluctuations. Abstract Ocean-atmosphere simulations corroborate the relationship between tropical Atlantic subsurface heat and salt storage driven by Salinity Maximum Water (SMW) and deglacial perturbations of the Atlantic Meridional Overturning Circulation (AMOC). Whether AMOC variability of the last glacial cycle affected SMW export into the tropical West Atlantic remained yet elusive. In order to assess the sensitivity of the tropical hydrography during abrupt and rapid glacial climatic and oceanic perturbations, we present century-resolving foraminifera-based subsurface (~200 m water depth) temperature and salinity reconstructions from Tobago Basin core M78/1–235-1. The proxy records were interpreted in terms of the closely related development of the North Brazil Current (NBC) and the North Atlantic Subtropical Gyre (STG) from ~37 to 30 ka BP, and in relation to their deglacial developments. Prior to ~32.8 ka BP, the cyclic variations in subsurface conditions were attributed to the NBC, which acted in line with a recurrent intensification and relaxation of the trade winds, subtle migrations of the Intertropical Convergence Zone, and the related moisture transport across Central America. Major and rapid re-organizations of the tropical Atlantic upper ocean-atmosphere system took place at ~32.8 ka BP and ~ 21.8 ka BP, unmirrored by major AMOC changes. Thresholds for sufficient heat and salinity accumulation in the STG to allow for formation and intensified subsurface dispersal of SMW were not achieved before late HS1, when AMOC weakening, according tropical heat backlog and surface warming by maximum Northern Hemisphere insolation acted together.

Mangroves are key ecosystems which respond to global changes in tropical and subtropical regions worldwide. We describe late Holocene mangroves that established close to the southernmost limit (28°S) for this type of ecosystem in South America. Our findings are based on a C dated core obtained from Babitonga Bay, Santa Catarina State, Brazil (26°12′S, 48°33′W). Analysis of palynology, sedimentary facies, isotopic and elemental data shows that mangrove establishment took place ~500 yrs. B.C.E., following an increase in humidity, and expanded further during the Roman Warm Period and at the end of Dark Age Cold Period. Mangrove and precipitation proxies records appear to be sensitive to rainfall patterns imposed both by the expansion/retraction of the Intertropical Convergence Zone and also the interaction with the South Atlantic Subtropical Anticyclone which affects coastal region due to sea surface temperature variations., The authors thank the Coastal Dynamic Laboratory (LADIC-UFPA) , C-14 Laboratory of the Center for Nuclear Energy in Agriculture (CENA-USP) , University of Joinville (UNIVILLE) and Radiocarbon Laboratory (LAC-UFF) for all infrastructure and support. We also thank three anonymous Reviewers and Prof. H. Falcon-Lang for their constructive comments. The first and third author thanks Brazilian Council for Technology and Science-CNPq for fellowship (process 131813/2016-1 , 165911/2015-8 and 305074/2017-2 ). This study was financed by CNPq ( 445111/2014-3 , 405060/2013- 0 ) and FAPESP ( 2011/00995-7 , 2017/03304-1, and 2020/13715-1 ). This study also was financed in part by the Coordenação de Aperfeiçoamento de Pessoal Nível Superior – Brazil (CAPES) – Finance Code 001 .

Author(s): Hwang, YT; Tseng, HY; Li, KC; Kang, SM; Chen, YJ; Chiang, JCH | Abstract: This study investigates the transient responses of atmospheric energy and momentum fluxes to a time-invariant extratropical thermal heating in an atmospheric model coupled to an aquaplanet mixed layer ocean with the goal of understanding the mechanisms and time scales governing the extratropical-to-tropical connection. Two distinct stages are observed in the teleconnection: 1) A decrease in the meridional temperature gradient in midlatitudes leads to a rapid weakening of the eddy momentum flux and a slight reduction of the Hadley cell strength in the forced hemisphere. 2) The subtropical trades in the forced hemisphere decrease and reduce evaporation. The resulting change to sea surface temperature leads to the development of a cross-equatorial Hadley cell, and the intertropical convergence zone shifts to the warmer hemisphere. The Hadley cell weakening in the first stage is related to decreased eddy momentum flux divergence, and the response time scale is independent of the mixed layer depth. In contrast, the time taken for the development of the cross-equatorial cell in the latter stage increases as the mixed layer depth increases. Once developed, the deep tropical cross-equatorial cell response is an order of magnitude stronger than the initial subtropical response and dominates the anomalous circulation. The analysis combines the momentum and energetic perspectives on this extratropical-to-tropical teleconnection and moreover shows that the subtropical circulation changes associated with the momentum budget occur with a time scale that is distinct from the deep tropical response determined by the thermal inertia of the tropical ocean.