2025-B7 Algal tracers of southeast Greenland meltwater and sea ice dynamics 

Overview

The melt dynamics of the Greenland Ice Sheet (GrIS) has major impacts on global sea level, sea ice conditions and polar oceanography through the delivery of fresh meltwater to the high-latitude North Atlantic. Due to complex ice sheet dynamics this process is one of the most uncertain components of the Earth System but can be improved by the generation of ‘proxy’ records of past ice sheet dynamics preserved in the marine sedimentary record.  

The project will work on an exceptional new set of sedimentary records from International Ocean Discovery Program Expedition 395 to constrain sea ice cover and ice sheet meltwater pulses using two novel organic biomarker techniques. The first will generate records of the C37:4 alkenone produced by sea-ice Isochrysidales (Wang et al. 2021). This biomarker is predominantly produced by a newly-identified group of sea-ice algae within the Isochrysidales order of marine haptophytes. Although other haptophyte-derived alkenones are routinely used for sea surface temperature (SST) estimation in the open ocean (e.g. Tierney & Tingley, 2018), the highly promising new sea ice proxy has not been applied to address key questions of Pleistocene sea ice dynamics and extent. Here we propose to use it to determine sea ice furthest extent off the southeast Greenland margin through the late Pleistocene. In intervals with little sea ice influence, the project will determine SSTs using traditional alkenone methods (ratio of C37:2 : C37:3). The project will also work closely with modern haptophyte geneticists (Bendif) and biologists (Wheeler) to interpret the fossil and proxy record of this novel group in the light of the latest phylogenies and a biological understanding of the sea-ice algal life cycle. 

As well as the C37:4 alkenone sea ice proxy, the same biomarker extractions will be used to determine the hydrogen isotopes of generic algal fatty acid biomarkers (δ2HFA) as a proxy for salinity and glacial meltwater pulses (Ashley et al. 2021). Such ‘meltwater pulses’ are characteristic of rapid ice sheet retreat or collapse and will be integrated with the sedimentological studies of other scientists within Expedition 395 to constrain the nature, duration and sediment provenance of these pulses.  

Figure 1. Bathymetric map of the NE Atlantic Ocean, Nordic Seas and Arctic Ocean. Red, orange, and blue arrows indicate surface, intermediate and deep ocean currents respectively. Deep ocean sediment cores spanning the mPWP are highlighted in yellow, including the critical new sites that will be a focus of this study: IODP Expedition 395 Sites U1562, U1564 and U1602.