Tuesday January 25, 2022, 1pm GMT+1

Lena M. THÖLE^1*, Peter D. NOTEBOOM^2,3 Suning HOU¹, Ruijan WANG⁴, Senyan NIE⁴, Elisabeth MICHEL⁵, Isabel SAUERMILCH¹, Fabienne MARRET⁶, Francesca SANGIORGI¹, Peter K. BIJL¹

Closing the Antarctic Void: Tighter Constraints on Biogeographic Affinities of Modern Dinoflagellate Cyst Assemblages in the Southern Ocean with Implications for Sea Surface Temperatures and Sea Ice Reconstructions 

¹ Department of Earth Sciences, Utrecht University, Utrecht, the Netherlands
² Institute for Marine and Atmospheric Research Utrecht, Utrecht, the Netherlands
³ Centre for Complex System Studies, Utrecht University, Utrecht, the Netherlands
⁴ State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
⁵ Laboratoire des Sciences du Climate et de l’Environnement, LSCE/IPSL, University de Paris-Saclay, Gif-sur-Yvette, France
⁶ Department of Geography and Planning, University of Liverpool, Liverpool, United Kingdom
^* l.m.thole@uu.nl 

Dinoflagellate cyst assemblages are used to reconstruct paleosurface ocean conditions such as sea surface temperature (SST), nutrients or sea ice for Antarctic Circumpolar Current-specific zones and fronts. Yet, a low surface sediment sample coverage in ice-proximal sites increases the uncertainty in polar environments and limits the use of dinocyst assemblages as sea ice proxy.
Here, we present a new dataset (n = 73) of surface sediment dinoflagellate cyst assemblages from ice-proximal locations around Antarctica. We add this to previously published data for the Southern Hemisphere (now 655 samples) to capture the distribution along the full range of environmental gradients. We perform k-means clustering on an ice-proximal and the entire southern hemisphere data set to potentially distinguish regional ice-proximal and southern hemispheric latitudinal differences. We reproduce a similar clustering as found previously, with additional clusters in the AZ dominated by Selenopemphix antarctica or Islandinium minutum.
A part of the uncertainty in dinocyst-environment relationships has been ascribed to strong lateral particle transport in the Southern Ocean. To incorporate this potential influence, we compare environmental parameters of overlying surface waters for each cluster with those derived from Lagrangian particle tracking simulations in a high-resolution (1/12° horizontally) ocean model with 25 m/day sinking speed. In general, we find similarly constrained cluster-specific environmental parameters when lateral transport is considered.
Our results emphasize the potential of dinoflagellate cysts as valuable proxies for SST and sea ice in the Southern Hemisphere. Considering lateral particle transport better represents the source regions but does not change the assigned environmental parameters. This encourages future efforts to translate dinocyst assemblages into quantitative tools for paleoceanographic reconstructions.