Abrupt deglacial changes in Atlantic Water properties entering the Arctic—Resolving temperature and freshwater influences and their relationship to ocean circulation

Project Description

Background: 
Abrupt climate events, involving changes in the coupled atmospheric-ocean-cryosphere system (e.g. Li and Born, 2019), are a persisting feature of Pleistocene glaciation (Hodell et al., 2022).  Despite their prominence, a mechanistic understanding of their origins remains elusive.  For example, it is still not known how and why North Atlantic Deep Water production changes and whether the events are forced by freshwater or arise spontaneously (e.g. Peltier and Vettoretti, 2014; Li and Born, 2019).   

The Younger Dryas, the most recent of these abrupt events, has long been hypothesized to be forced directly by freshwater (Broecker et al., 1989).  If, as hypothesized (Tarasov and Peltier, 2005), this freshwater was routed to the Arctic it could have had a large impact on density, and thus production, in deep water formation regions (Condron and Winsor, 2012).  New, high-resolution reconstructions from the northern Barents Sea along the flow path of Atlantic Water entering the Arctic depict prominent 18O decreases in planktic and benthic foraminifera during the Younger Dryas (YD) and Heinrich Stadial 1 (HS1) cold events.   Because foraminiferal 18O is influenced by both changes in temperature and 18Ow (salinity) these perturbations could be interpreted as 1) an abrupt 5-8°C warming in Atlantic Water due to AMOC decline in response to sea ice expansion, or 2) a freshening due to sudden meltwater input.  These interpretations have distinctly different implications for the roles that deep water, heat transport, and freshwater play in abrupt climate changes. These influences can be disentangled by applying clumped isotope thermometry (Eiler, 2007) to foraminifera; yielding direct estimates of ocean temperature and calculation of seawater isotopic composition.  

Scientific Problem/Question(s): 
Is the prominent anomaly in delta 18O reflecting a freshening or warming of Atlantic Water?  
Is the Younger Dryas (and HS1, time permitting) forced by FW?

Scientific Work (field/lab/analysis): 
Autumn (2022)-Spring (2023):  work with the (dated) cores where the foraminiferal 18O perturbations are documented—sample preparation and microscope work selecting foraminifera for analyses spanning the YD (and time permitting HS1) anomaly. 
Spring 2023: Clumped isotope analyses in FARLAB.  The co-registration of conventional 18O (Temperature and delta 18Ow) and clumped isotopes (delta47) from the same samples will be used to elucidate the influence of freshwater and temperature changes on Atlantic Water properties during the YD event.  
Spring 2023-Autumn 2023 Data analysis.

Courses relevant for this project: 
GEOV222 (10 credits), GEOV300 (5 credits), GEOV324 (5 credits) and GEOV231 (10 credits) 
Courses will furthermore be planned together between student and supervisor.