Audrey Morley

Ollscoil na Gaillimhe – University of Galway

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Yair Rosenthal

Rutgers Sexual and Reproductive Health and Rights

Ulysses S. Ninnemann

Bjerknes Centre for Climate Research

Michelle J. Curran

Ollscoil na Gaillimhe – University of Galway

Dakota Holmes

Ollscoil na Gaillimhe – University of Galway

Carsten Rühlemann

Federal Institute for Geosciences and Natural Resources

Michael Schulz

University of Bremen

Stefan Mulitza

University of Bremen

Christophe Colin

Geosciences Paris Sud

Tali L. Babila

Case Western Reserve University

André Paul

Islamic University

Cooperative Institutions

Ollscoil na Gaillimhe – University of Galway

University of Bremen

University of Bergen

Centre National de la Recherche Scientifique

Bjerknes Centre for Climate Research

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Rutgers, The State University of New Jersey

Royal Netherlands Institute for Sea Research

University of Southampton

Alzheimer's Association of Israel

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Raw data and interpolated raw data from proxy records of sediment core GeoB6007-1

Audrey Morley Michael Schulz Yair Rosenthal Stefan Mulitza André Paul

Sediment core

Proxy (statistics)

10.1594/pangaea.770708

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Audrey Morley

Abstract. 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.

Circumpolar deep water

10.5194/cp-2021-97-ac4

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Audrey Morley

Abstract. WhileÂ 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 surfaceâdeep phasing, advances our mechanistic understanding of, and elucidates antecedent conditions that can lead to, high-magnitude climate instability.

Circumpolar deep water

10.5194/cp-2021-97-ac2

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Age model, and raw data of bottom water temperatures (BWT) and stable oxygen isotopes of seawater reconstructions (Mg/Ca, δ18O) using the benthic foraminifera Hyalinea balthica from the Irish Continental Shelf

Michelle J. Curran Yair Rosenthal James D. Wright Audrey Morley

δ18O

10.1594/pangaea.907706

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The Holocene Thermal Maximum: A possible analogue for future Ocean-Atmosphere climate Dynamics?

EGUGA (2018)

Michelle Curran Audrey Morley James Wright Yair Rosenthal

Atmospheric Dynamics

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Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events?

Dakota Holmes Audrey Morley

Abrupt climate events are generally believed to be characteristic of glacial (intermediate-to-large cryosphere) climate states, requiring either sizeable ice-sheets or large freshwater pulses to act as triggers for abrupt climate changes to occur. Amplification occurs when these triggers bear upon the Atlantic Meridional Overturning Circulation (AMOC). However, the focus on glacial climate states in abrupt climate change research has led to an underrepresentation of research into interglacial periods. It thus remains unclear whether high-magnitude climate variability requires large cryosphere-driven feedbacks or whether it can also occur under low ice conditions. Here we present a high resolution analysis of surface and deep water components of the AMOC spanning the transition from Marine Isotope Stage (MIS) 19c to 19a to test if orbital boundary conditions similar to our current Holocene can accommodate abrupt climate events. Sediment core DSDP 610B (53&#176;13.297N, 18&#176;53.213W), located approximately 700-km west of Ireland, was specifically chosen due to its high sedimentation rate during interglacial periods, excellent core recovery over the Quaternary and its unique geographical location. Above the core site, the dominant oceanographic feature is the North Atlantic Current and at 2417-m water depth, 610B is influenced by Wyville Thomson Overflow Water flowing southwards. A multiproxy approach including paired grain size analysis, planktic foraminifer assemblage counts, and ice-rafted debris counts within the same samples allows us to resolve the timing between both surface and bottom components of the AMOC and their response to abrupt climate events during MIS-19 in the eastern subpolar gyre. This study is societally relevant as future freshwater inputs from a melting Greenland ice sheet may impact ocean circulation, potentially causing shifts in climate for many European countries.

Abrupt climate change

Ice core

Climate state

Marine isotope stage

Meltwater

Iceberg

Climate pattern

10.5194/egusphere-egu2020-19225

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Deciphering the Signal of Arctic Climate Change

Audrey Morley Markus Raitzsch Jelle Bijma Szabina Karancz Michal Kučera

Whether or not Arctic regions remain(ed) a carbon sink or source to the atmosphere during rapidly warming climates (in the past) is a fundamental question with regards to future global warming and ocean acidification. The boron isotopic composition of planktonic foraminiferal shell calcite (&#948;11BCc) can potentially provide valuable information of past seawater pH if information on a second carbonate system parameter, temperature, and salinity is available. However, most applications of palaeoceanographic proxies to the cold polar oceans are limited due to a paucity of calibration data, limited information on the calcification habitat, and secondary effects of the carbonate system on the temperature recorded by Mg/Ca values measured in the dominant Arctic species Neogloboquadrina pachyderma sinistral (NPS). Here we present a new Multi-Collector Inductively Coupled Mass Spectrometry (MC-ICPMS) &#948;11B dataset measured on live NPS collected via plankton tows from the Labrador Sea and Baffin Bay. We compare our results with &#948;11Bborate derived from pH measurements, &#948;13C DIC seawater values, temperature and salinity collected at the time and depth the foraminifera calcified. To quantify the control of low carbonate ion concentration on Mg/Ca derived temperatures we measured B/Ca alongside Mg/Ca in the calibration dataset. We are thus able to present a new geochemical correction scheme that can isolate non-thermal controls on the Mg/Ca-temperature relationship for NPS, allowing us for the first time the reconstruction of carbonate system parameters in the Arctic Ocean.

Ocean Acidification

10.5194/egusphere-egu2020-19481

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Are Cryosphere-Driven Feedbacks a Requisite for Abrupt Climate Events? (Site U610, DSDP Leg. 94)

Dakota Holmes David De Vleeschouwer Audrey Morley

Abrupt climate events are important features of glacial climate scales on centennial and millennial timescales. These events' mechanistic trigger is often ascribed to either ice sheet-related feedback mechanisms or large freshwater pulses. In both cases, amplification occurs when these triggers bear upon the Atlantic Meridional Overturning Circulation (AMOC). However, the focus on glacial climate states in abrupt climate change research has led to an underrepresentation of research into interglacial periods. It thus remains unclear whether high-magnitude climate variability requires large cryosphere-driven feedbacks or whether it can also occur under low ice conditions. Using sediment core DSDP U610B (53&#176;13.297N, 18&#176;53.213W) located in the Rockall Trough, we present a high-resolution analysis of surface and deep water components of the AMOC spanning the transition from Marine Isotope Stage (MIS) 19.3 to 19.1 to test if orbital boundary conditions similar to our current Holocene can accommodate abrupt climate events. Above the core site, the dominant oceanographic feature is the North Atlantic Current and at 2417-m water depth, U610 is influenced by Wyville Thomson Overflow Water flowing southwards. We utilise a multiproxy approach including paired grain size analysis, planktic foraminifera assemblage counts, and ice-rafted debris counts within the same samples allowing us to resolve the timing between both surface and bottom components of the AMOC and their response to abrupt climate events during MIS-19 in the eastern subpolar gyre. We also present for the first time a new splice and composite depth scale for Site U610. Based on preliminary results, rapid shifts in both deep overflow and surface climate characterise this period.

Abrupt climate change

paleoceanography

Marine isotope stage

Iceberg

10.5194/egusphere-egu21-8237

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Audrey Morley

Abstract. Abrupt climate events are generally attributed as a characteristic of glacial (intermediate-to-large cryosphere) climate states. While a large cryosphere may be a necessary boundary condition for millennial-scale events to persist, it remains unclear whether high-magnitude climate variability is purely a glacial phenomenon requiring cryosphere-driven feedbacks. High-resolution climate records are used to portray North Atlantic climate's progression through low-ice, interglacial boundary conditions of Marine Isotope Stage (MIS) 11c into the glacial inception. We show that this period is marked by rapid shifts in both deep overflow and surface climate. The reorganization between polar and Atlantic waters 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 glacial and interglacial boundary conditions, we find that a reduction in deep water precedes surface hydrographic change. The existence of surface and deep ocean events during an interglacial, with similar magnitudes, abruptness, and surface-deep phasing as their glacial counterparts, alters our concept of “warm” climate stability and the requisite cryospheric thresholds and feedbacks for it.

Climate state

Abrupt climate change

10.5194/cp-2021-97-ac1

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Audrey Morley

Abstract. Recent investigations into Marine Isotope Stage (MIS) 11 (424–403 ka), an unusually long and warm interglacial of the Quaternary Period, have found that the Atlantic Meridional Overturning Circulation remained strong while background melting of the Greenland Ice-Sheet (GIS) was high, and resulted in a fresh and cold surface ocean in the Nordic Seas. These investigations support the hypothesis that deep-water formation may not be as susceptible to future GIS melting as previously thought. Here we test this hypothesis and present a palaeoceanographic investigation of a freshwater-related abrupt climate event recorded in the eastern North Atlantic during peak interglacial conditions (~412 ka), when the GIS was as small or smaller than today. Using sediment core DSDP-610B recovered from the western Rockall Trough we reconstruct the evolution of Nordic Seas Deep-Water (NSDW) using benthic carbon isotope, Neodymium isotopes, and grain-size analysis paired with end-member modelling. Further, a combination of planktonic foraminiferal assemblage census and Ice-Rafted Debris counts allow us to reconstruct surface water properties including temperature and the movement of oceanic fronts throughout this event. Our results demonstrate that a reduction of NSDW only occurs once GIS melt and polar freshwater reaches subpolar latitudes. We hypothesise that the reorganisation of fresh and cold surface waters from the Nordic Seas into the subpolar North Atlantic was responsible for an AMOC-related cold event centred at 412 ka. Placing our results in the palaeogeographical context of the North Atlantic Region we tentatively propose that the ocean-atmosphere climate dynamics linking the Nordic Seas with the subpolar North Atlantic played and will play a crucial role for the stability of NSDW formation in the future, considering the enhanced melting and overall hydrological cycle at high Northern latitudes predicted for future climate scenarios.

10.5194/cp-2023-101-ac1

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