Reorganization of Atlantic Waters at sub-polar latitudes linked to deep-water overflow in both glacial and interglacial climate states

While a large cryosphere may be a necessary boundary condition for millennial-scale events to persist, a growing body of evidence from previous interglacial periods suggests that high-magnitude climate events are possible during low-cryosphere climate states. However, the full spectrum of variability, and the antecedent conditions under which such variability can occur, have not been fully described. As a result, the mechanisms generating high-magnitude climate variability during low-cryosphere boundary conditions remain unclear. In this study, high-resolution climate records from Deep Sea Drilling Project (DSDP) site 610 are used to portray the North Atlantic climate's progression through low ice, boundary conditions of Marine Isotope Stage (MIS) 11c into the glacial inception. We show that this period is marked by two climate events displaying rapid shifts in both deep overflow and surface climate. The reorganization between Polar Water and Atlantic Water at subpolar latitudes appears to accompany changes in the flow of deep water emanating from the Nordic Seas, regardless of magnitude or boundary conditions. Further, during both intermediate and low ice boundary conditions, we find that a reduction in deep water precedes surface hydrographic change. The existence of surface and deep-ocean events, with similar magnitudes, abruptness, and surface–deep phasing, advances our mechanistic understanding of, and elucidates antecedent conditions that can lead to, high-magnitude climate instability.publishedVersio

Reorganization of Atlantic Waters at sub-polar latitudes linked to deep-water overflow in both glacial and interglacial climate states

While a large cryosphere may be a necessary boundary condition for millennial-scale events to persist, a growing body of evidence from previous interglacial periods suggests that high-magnitude climate events are possible during low-cryosphere climate states. However, the full spectrum of variability, and the antecedent conditions under which such variability can occur, have not been fully described. As a result, the mechanisms generating high-magnitude climate variability during low-cryosphere boundary conditions remain unclear. In this study, high-resolution climate records from Deep Sea Drilling Project (DSDP) site 610 are used to portray the North Atlantic climate's progression through low ice, boundary conditions of Marine Isotope Stage (MIS) 11c into the glacial inception. We show that this period is marked by two climate events displaying rapid shifts in both deep overflow and surface climate. The reorganization between Polar Water and Atlantic Water at subpolar latitudes appears to accompany changes in the flow of deep water emanating from the Nordic Seas, regardless of magnitude or boundary conditions. Further, during both intermediate and low ice boundary conditions, we find that a reduction in deep water precedes surface hydrographic change. The existence of surface and deep-ocean events, with similar magnitudes, abruptness, and surface–deep phasing, advances our mechanistic understanding of, and elucidates antecedent conditions that can lead to, high-magnitude climate instability.publishedVersio

Coupled evolution of temperature and carbonate chemistry during the Paleocene–Eocene; new trace element records from the low latitude Indian Ocean

This is the final version. Available on open access from Elsevier via the DOI in this recordThe early Paleogene represents the most recent interval in Earth’s history characterized by global greenhouse warmth on multi-million year timescales, yet our understanding of long-term climate and carbon cycle evolution in the low latitudes, and in particular the Indian Ocean, remains very poorly constrained. Here we present the first long-term sub-eccentricity-resolution stable isotope (δ13 30 C and δ 18 O) and trace element (Mg/Ca and B/Ca) records spanning the late Paleocene–early Eocene (~58– 53 Ma) across a surface–deep hydrographic reconstruction of the northern Indian Ocean, resolving late Paleocene 405-kyr paced cyclicity and a portion of the PETM recovery. Our new records reveal a long-term warming of ~4–5°C at all depths in the water column, with absolute surface ocean temperatures and magnitudes of warming comparable to the low latitude Pacific. As a result of warming, we observe a long-term increase in δ 18 Osw of the mixed layer, implying an increase in net evaporation. We also observe a collapse in the temperature gradient between mixed layer- and thermocline-dwelling species from ~57–54 Ma, potentially due to either the development of a more homogeneous water column with a thicker mixed layer, or depth migration of the Morozovella in response to warming. Synchronous warming at both low and high latitudes, along with decreasing B/Ca ratios in planktic foraminifera indicating a decrease in ocean pH and/or increasing dissolved inorganic carbon, suggest that global climate was forced by rising atmospheric CO2 concentrations during this time.European Consortium for Ocean Research Drilling (ECORD)International Association of Sedimentologists (IAS)NSFNatural Environment Research Council (NERC

Boron/Calcium in planktonic foraminifera: proxy development and application to the Paleocene-Eocene boundary

Climate transitions on recent and geologic timescales are linked to perturbations in atmospheric carbon dioxide concentrations (pCO2). Records of ocean carbonate chemistry allow us to investigate the role of CO2 during past climate events but are limited by the availability of paleo-proxies. This thesis presents the development and calibration of Boron/Calcium (B/Ca) in planktonic foraminifera as a proxy for surface ocean carbonate chemistry from sediment traps and modern surface sediments. The B/Ca proxy is then used to reconstruct surface ocean acidification across the Paleocene-Eocene boundary (~55.8 Myr). Observations of B/Ca in the surface dwelling planktonic foraminifer Globigerinoides ruber white from the Oceanic Flux Program (OFP) sediment trap time-series located near Bermuda are used to suggest that the photosynthetic activity of symbiotic algae within the living foraminifer modify the internal pH relative to the ambient seawater, thereby influencing the B/Ca recorded in the calcitic test (Chapter Two). I hypothesize that the apparent covariance between G. ruber B/Ca and the temperature at the OFP site is due to the seasonal change in incident light affecting the symbiont activity, which can increase the internal pH during calcification from seawater by ~0.2-0.3 units. Measurements of B/Ca and δ11B in different species of planktonic foraminifera from globally distributed core-top sediments reveal that symbiotic foraminifera are offset from the theoretically predicted equilibrium with seawater (Chapter Three). I find no significant temperature effect on B/Ca and the departure from equilibrium for symbiont-bearing species is attributed to biological effects. I provide empirical calibrations for thermocline and deep-dwelling planktonic foraminifera as being primarily controlled by seawater [(〖"B(OH)" 〗_"4" ^"-" )⁄(〖"HCO" 〗_"3" ^"-" )]. Paired isotopic (δ13C, δ18O) and elemental (Mg/Ca, B/Ca) measurements are applied to reconstruct the relative timing and magnitude of environmental changes across the Paleocene-Eocene boundary, occurring ~55.8 Myr using sections from ODP Leg 174AX sites at Bass River and Ancora. Reconstructions of ocean temperature (Mg/Ca) and carbonate chemistry (δ13C and B/Ca) from planktonic foraminifera document an abrupt and significant decrease in B/Ca ratios, coincident with δ13C records and the concomitant ~6-8°C warming. The synchronous changes in all three proxies do not support the occurrence of significant precursor warming or carbon release argued elsewhere.Ph. D.Includes bibliographical referencesby Tali Lea Babil

Boron-CO2 workshop: Testing and extending the limits of the foraminiferal boron proxy for seawater pH and atmospheric CO2 reconstructions

Workshop report - Bergen, Norway, 4 September 2022 Atmospheric carbon dioxide (CO2) is the key driver of global temperatures over geological time, but calculating the exact sensitivity of Earth’s climate to CO2, and hence the trajectory of anthropogenic climate change, requires accurate quantification of past CO2. Determining past CO2 and fluxes among Earth's carbon reservoirs is difficult, particularly prior to ice-core records of the last 800 kyrs. Attempts have been made to compile multi-proxy atmospheric CO2 proxy data through time (Foster et al. 2017; Hönisch 2021; Rae et al. 2021) which have gained considerable traction, including in the Intergovernmental Panel on Climate Change reports (IPCC 2021). However, many of these compilations can include inaccuracies and apparent contradictions arising from differing assumptions and auxiliary inputs used when translating proxy data to CO2. To move forward as a community, ensuring the robustness of future CO2 data contributions and reducing noise in a crucial dataset, such inconsistencies must be minimized, and uncertainties systematically accounted for (Fig. 1)

Sea surface temperatures from the Western Pacific Warm Pool across the last 17kyrs

The Indo-Pacific Warm Pool (IPWP) contains the warmest surface ocean waters on our planet. Changes in the extent and position of the IPWP likely impacted the tropical and global climate in the past. To put recent ocean changes into a longer temporal context, we present new paleoceanographic sea surface temperature reconstructions from off Papua New Guinea (RR1313-23PC: 4.4939°S, 145.6703°E, 712 m water depth) which is at the heart of the Western Pacific Warm Pool (WPWP), which is the warmest region within the IPWP, across the last 17,000 years. A new surface temperature dataset from the northeast South China Sea is also presented (ODP1144: 20.053°N, 117.4189°E; water depth 2037 m). In both locations we use Mg/Ca measurements on G.ruber s.s. (white) to calculate sea surface temperatures

Net community production in the northeastern Chukchi Sea

To assess the magnitude, distribution and fate of net community production (NCP) in the Chukchi Sea, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), and particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured during the spring and summer of 2004 and compared to similar observations taken in 2002. Distinctive differences in hydrographic conditions were observed between these two years, allowing us to consider several factors that could impact NCP and carbon cycling in both the Chukchi Shelf and the adjacent Canada Basin. Between the spring and summer cruises high rates of phytoplankton production over the Chukchi shelf resulted in a significant drawdown of DIC in the mixed layer and the associated production of DOC/N and POC/N. As in 2002, the highest rates of NCP occurred over the northeastern part of the Chukchi shelf near the head of Barrow Canyon, which has historically been a hotspot for biological activity in the region. However, in 2004, rates of NCP over most of the northeastern shelf were similar and in some cases higher than rates observed in 2002. This was unexpected due to a greater influence of low-nutrient waters from the Alaskan Coastal Current in 2004, which should have suppressed rates of NCP compared to 2002. Between spring and summer of 2004, normalized concentrations of DIC in the mixed layer decreased by as much as 280 ?mol kg?1, while DOC and DON increased by ?16 and 9 ?mol kg?1, respectively. Given the decreased availability of inorganic nutrients in 2004, rates of NCP could be attributed to increased light penetration, which may have allowed phytoplankton to increase utilization of nutrients deeper in the water column. In addition, there was a rapid and extensive retreat of the ice cover in summer 2004 with warmer temperatures in the mixed layer that could have enhanced NCP. Estimates of NCP near the head of Barrow Canyon in 2004 were ?1500 mg carbon (C) m?2 d?1 which was ?400 mg C m?2 d?1 higher than the same location in 2002. Estimates of NCP over the shelf-break and deep Canada Basin were low in both years, confirming that there is little primary production in the interior of the western Arctic Ocean due to near-zero concentrations of inorganic nitrate in the mixed layer