Yugeng Chen’s research while affiliated with Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung and other places

Paleo‐proxy data indicate that during the Last Glacial Maximum (LGM), the volume of Antarctic Bottom Water (AABW) in the Atlantic was nearly four times greater than it is today. We employed an ocean‐only model to simulate the galcial ocean and sea‐ice conditions. Our simulations reveal two key mechanisms driving its greater volume. First, while present‐day sea ice formation is driven largely by seasonal changes, the glacial mechanism is the substantial export of sea ice toward lower latitudes. The glacial sea ice formation was more than quadruple current levels, providing a steady source of Dense Shelf Water (DSW) crucial for AABW expansion. Second, weaker mixing between North Atlantic Deep Water (NADW) and AABW during the LGM allows the latter to maintain the colder, denser properties of its DSW origin. Together, these factors clarify how glacial conditions supported significantly greater AABW volumes, aligning well with paleo‐proxy evidence.

The deep Southern Ocean (SO) circulation plays a key role in the storage and release of CO2 in Earth’s climate system. The uptake and release of CO2 strongly depend on the redistribution of well and poorly ventilated deep ocean water masses. Recently, evidence was found for possible stronger Pacific deep water overturning and subsequent intrusion into the SO during periods of reduced AMOC. Here, we present new authigenic neodymium isotope data (ɛNd) from two sites within the Atlantic sector of the SO to assess the distribution of water masses during the past 150 ka. PS 1768-8 (3299 m) and ODP 1093 (3624 m) feature unradiogenic interglacial ɛNd-signatures, which are typical for present-day Weddell Sea sourced Antarctic Bottom Water (AABW) (ɛNd ~ − 8.6). During peak glacial periods, radiogenic ɛNd-values ranging from ~ − 2.5 to − 3.5 are recorded. This may be the result of either a strong Pacific or benthic flux influence on the Nd budget in the Atlantic sector of the SO. However, an ocean circulation model indicates no stronger Pacific influence during glacials. Thus, we suggest that an increase in benthic flux influences the SO Nd budget, which is modulated by ACC strength. The more stratified and more sluggish deep water supports decreased vertical mixing and increased glacial carbon storage without the intrusion of poorly ventilated Pacific waters. The occurrence of highly radiogenic glacial bottom water or porewater signatures requires reassessment of the glacial Southern Hemisphere ɛNd-endmember for water mass sourcing reconstructions in the glacial Atlantic.

The Bølling-Allerød (BA) period, characterized by rapid climate warming, provides a unique opportunity to study the dynamics of the Atlantic Meridional Overturning Circulation (AMOC). Despite expectations that the AMOC would weaken due to substantial meltwater input from Northern Hemisphere ice sheets, proxy data evidence suggests it unexpectedly strengthened during this transition. In this study, we examine the previously unconsidered role of tides during the BA period through a series of ocean circulation model simulations. Our findings indicate that enhanced tidal mixing during the BA significantly contributed to the rapid amplification of the AMOC, also increasing its resilience to freshwater inputs from deglaciation. This research provides a novel explanation for the AMOC's rapid amplification and resilience during the BA period, emphasizing the critical role of tides in enhancing our understanding of abrupt climate transitions and future climate change.

During the Last Glacial Maximum (LGM), tidal dissipation was about 3-fold higher than today, which could have led to a considerable increase in vertical mixing. This increase might have enhanced the glacial Atlantic Meridional Overturning Circulation (AMOC), contradicting the shoaled AMOC indicated by paleoproxies. Here, we conduct ocean model simulations to investigate the impact of background climate conditions and tidal mixing on the AMOC during the LGM. We successfully reproduce the stratified ocean characteristics of the LGM by accurately simulating the elevated salinity of the deep sea and the rapid temperature decrease in the ocean's upper layers. Our findings indicate that the shoaled glacial AMOC is mainly due to strong glacial-ocean stratification, regardless of enhanced tidal dissipation. However, glacial tidal dissipation plays a critical role in the intensification of Antarctic Bottom Water (AABW) during the LGM. Given the critical role of the AMOC in (de-)glacial climate evolution, our results highlight the complex interactions of ocean stratification and tidal dissipation that have been neglected so far.

During the Last Glacial Maximum (LGM), tidal dissipation was about threefold higher than today, which could have led to a considerable increase in vertical mixing. This would enhance the glacial Atlantic Meridional Overturning Circulation (AMOC), contradicting the shoaled AMOC as indicated by paleo proxies. Here, we conduct ocean model simulations to investigate the impact of background climate conditions and tidal mixing on the AMOC during LGM. We successfully reproduce the stratified ocean characteristic of the LGM by accurately simulating the elevated salinity of the deep sea and the rapid temperature decrease in the ocean's upper layers. Our findings indicate that show that the shoaled glacial AMOC is mainly due to strong glacial ocean stratification, irrespective of enhanced tidal dissipation. However, glacial tidal dissipation plays a critical role in the intensification of the AABW during the LGM. Given the critical role of AMOC in (de-)glacial climate evolution, our results highlight the complex interactions of ocean stratification and tidal dissipation that have been neglected so far.