Description: Atmospheric CO2 and global climate are closely coupled. Since 800 ka CO2 concentrations have been up to 50% higher during interglacial compared to glacial periods. Because of its dependence on temperature, humidity, and erosion rates, chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition. Cooler and drier conditions and lower non-glacial erosion rates suppressed in situ chemical weathering rates during glacial periods. However, using systematic variations in major element geochemistry, Sr–Nd isotopes and clay mineral records from Ocean Drilling Program Sites 1143 and 1144 in the South China Sea spanning the last 1.1 Ma, we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials. We attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands. Our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for ~9% of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial–interglacial variation of ~80 ppmv. As a result, if similar magnitudes can be identified in other tropical shelf-slope systems, the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric CO2 during cold stages of the Quaternary. This in turn would have caused an intensification of glacial cycles.

Description: The cause of rapid hydrological changes in the tropical West Pacific during the last deglaciation remains controversial. In order to test whether these changes were triggered by abrupt climate change events in the North Atlantic Ocean, variations in precipitation during the last deglaciation (18–10 ka) were extracted from proxy records of chemical weathering and terrigenous input in the western Philippine Sea (WPS). The evolution of chemical weathering and terrigenous input since 27 ka was reconstructed using the chemical index of alteration (CIA), elemental ratios (K/Al, TOC/TN and Ti/Ca), δ13Corg, terrigenous fraction abundance and flux data from International Marine Global Change Study Program (IMAGES) core MD06-3054 collected on the upper continental slope of eastern Luzon (northern Philippines). Sediment deposited during the Last Glacial Maximum (LGM) shows weathering equal to or slightly greater than Holocene sediment in the WPS. This unusual state of chemical weathering, which is inconsistent with lower air temperatures and decreased precipitation in Luzon during the LGM, may be due to reworking of poorly consolidated sediments on the eastern Luzon continental shelf during the LGM sea-level lowstand. Rapid changes in chemical weathering, characterized by higher intensity during the Heinrich event 1 (H1) and Younger Dryas (YD) and lower intensity during the Bølling-Allerød (B/A), were linked to rapid variations in precipitation in the WPS during the last deglaciation. The higher terrigenous inputs during the LGM relative to those of the Holocene were controlled by sea-level changes rather than precipitation. The terrigenous inputs show a long-term decline during the last deglaciation, punctuated by brief spikes during the H1 and YD related to sea-level rises and rapid precipitation changes in the WPS, respectively. The proxy records of chemical weathering and terrigenous input from eastern Luzon suggest high rainfall during the H1 and YD events, consistent with inferred rainfall patterns based on Fe/Ca records from offshore Mindanao. Rapid precipitation changes in the WPS did not coincide with migrations of the Intertropical Convergence Zone (ITCZ) but, rather, were related to state shifts of the El Niño-Southern Oscillation (ENSO) during the last deglaciation. Based on proxy records and modeling results, we argue that the Atlantic meridional overturning circulation (AMOC) controlled rapid precipitation changes in the tropical West Pacific through zonal shifts of ENSO or meridional migration of the ITCZ during the last deglaciation. Our findings highlight the dominant role of the North Atlantic Ocean in the tropical hydrologic cycle during the last deglaciation.

Description: Highlights • High-resolution deep-water record for Pliocene western tropical Pacific. • Changes in NADW production at ∼4.6 Ma and ∼2.7 Ma influenced Pacific • These changes controlled a seesaw fluctuation between deep Pacific and Atlantic oceans. • Antarctic ice-sheet/sea-ice expansions influenced deep Pacific • These ice-mass changes resulted in long-term decline during late Pliocene. Abstract Quantifying changes in seawater carbonate chemistry is crucial to deciphering of patterns and drivers of the oceanic carbon cycle and climate change. Here, we present a new deep-water carbonate ion saturation state record for the Pliocene western tropical Pacific, reconstructed from the size-normalized weight of the planktonic foraminifer Trilobatus sacculifer of IODP Site U1490. A steep decline in deep-water occurred at ∼4.6 Ma synchronous to the enhanced production of North Atlantic Deep Water (NADW) related to the closure of the Panamanian Gateway. Subsequently, at the onset of the Northern Hemisphere glaciation at ∼2.7 Ma the weakening of NADW formation resulted in a deep-water peak. The changes in NADW production rate likely controlled a seesaw-like fluctuation in deep-water between the Pacific and Atlantic oceans. During the late Pliocene (∼3.8–2.8 Ma), Antarctic ice-sheet/sea-ice expansions sequestered CO2 in the deep Pacific through ventilation of the deep watermass, leading to a long-term decrease in deep Pacific . We infer that fluctuating NADW production rates at ∼4.6 Ma and ∼2.7 Ma influenced inter-basinal fractionation of deep-ocean carbon between the Atlantic and Pacific, and that deep Pacific carbon storage linked to expansions of Antarctic ice sheet/sea ice contributed to the lowering of atmospheric pCO2 and global cooling during the late Pliocene.

Description: Highlights • Accurate age model during Pliocene for site U1490 established • Co-variant nutricline depth and productivity in WPWP throughout Pliocene • Deeper nutricline and lower productivity during 4.8–3.5 Ma linked to CAS closure • Nutricline shoaling during 3.5–3.0 Ma due to restriction of Indonesian Seaway Abstract The tropical Pacific played an important role in modulating global climate change during the Pliocene. Studies of tropical Pacific sea surface temperatures covering the period from the Pliocene onwards indicate that changes in the thermal mean state over the tropical Pacific can significantly influence global climate feedbacks and connect the high- and low-latitude climates. Tropical productivity fluctuations are a significant mechanism with respect to the operation of the global carbon cycle. Yet, temporal changes in primary productivity are not well constrained in the western Pacific warm pool (WPWP), where the ocean–climate system is not dominated by upwelling systems. Furthermore, the role of nutricline dynamics in forcing productivity over tectonic timescales remains uncertain. Here we use relatively high-resolution foraminiferal carbon isotope records combined with Ba/Ti ratios obtained from International Ocean Discovery Program (IODP) Site U1490 in the WPWP to reconstruct nutricline depth and paleoproductivity over the period 5.1–2.6 Ma. Our records imply that nutricline and productivity variations were closely coupled over tectonic timescales, implying that the dynamics of the nutricline play a significant role in regulating productivity in the WPWP. The deeper nutricline and lower productivity during 4.8–3.5 Ma might have been fostered by the closure of the Central American Seaway through the thickening of the mixed layer in the WPWP. We relate the overall shallower nutricline and increased productivity during 3.5–3.0 Ma to the restriction of the Indonesian Seaway via the enhanced influence and upwelling of high-latitude southern-source waters.

Description: Analytical Chemistry DOI: 10.1021/acs.analchem.7b00091

Description: The East Asian winter monsoon (EAWM) significantly impacts living conditions in a large part of Asia, and therefore, it is important to understand its major driving mechanisms. Winter sea surface temperature (SST W ) and circulation in the southern Okinawa Trough are today both primarily controlled by the EAWM. Here we present a new SST W reconstruction for the last millennium based on a diatom record from sediment core MD05-2908, from the continental slope of the southern Okinawa Trough off northeastern Taiwan. Our reconstruction indicates that SST W varied between 14.1 and 19.6°C over the past 1,000 years. Changes in SST W in the southern Okinawa Trough correspond closely to the index of warm winters based on historical documents from the East Asian monsoon domain. This implies that our SST W record can be used to reconstruct EAWM variability during the last millennium. Comparisons with the reconstructed winter Arctic Oscillation (AO, developed from historical snow anomaly events in Eastern Asia) and Arctic sea ice cover reveal a significant positive correlation between the EAWM and AO during the time interval from 1000–1400 Common Era (C.E.), coinciding with reduced sea ice cover. However, there is no significant correlation with increased sea ice cover during the interval from 1400 to 1700 C.E. This suggests that the reduction in Arctic sea ice may periodically have played a role in strengthening the relationship between the EAWM and the AO during the last millennium and that the current and future reduction in Arctic sea ice may have significant consequences for the EAWM.

Description: El Niño/Southern Oscillation (ENSO) activity and the Pacific Walker Circulation are controlled by the zonal sea surface temperature (SST) gradient between the western and Eastern Equatorial Pacific (EEP) and the corresponding barometric difference. Variations in the zonal SST gradient since the early Pleistocene have primarily been triggered by changes in the SST in the Eastern Equatorial Pacific. However, the response of the ENSO-like long-term state to the cooling of the EEP and its coupling role with tropical Pacific climate changes are still not well established. Here we present a high-resolution grain-size record spanning the last 2.36 Myr, obtained from marine core sediment located in the West Philippine Sea in order to decipher the tropical pacific climate changes and reveal its controlling mechanism. By combining our data with other long-term climatic records from the Equatorial Pacific, we demonstrate that the cooling of SST and enhanced upwelling in the EEP resulted in the development of the Walker Circulation and increased monsoon precipitation in Luzon from 2.2 to 1.6 Myr, from 1.2 to 0.8 Myr and since 0.2 Myr ago. The progressive cooling of the high-latitudes in the Quaternary may be responsible for our observation here. A newly identified 100-kyr dominant period between 2.2 and 1.6 Myr in the ENSO-like modulated Pacific climate records indicates that the ENSO-like system may play a key role in facilitating or responding to the global climate changes.