Collaborative Research: Evolution of Arctic Water Column Hydrography during the Holocene Based on a Novel Instrumentation Combination

During the past few decades, the Arctic has warmed approximately twice as rapidly as the entire northern hemisphere, associated with substantial retreat and thinning of the Arctic sea-ice cover during the past decade. Associated with the Arctic warming and waning sea-ice cover is a reorganization of the surface and deep-water circulation of the Arctic Ocean, but understanding of the associated processes is limited. The early to mid-Holocene provides a post-glacial analogue of a seasonally ice-free Arctic Ocean, similar to scenarios that have been proposed for the next several decades. This early-mid Holocene sea ice minimum, 10?6 thousand years ago, is often attributed to changes in solar forcing. However, records providing information on upper Arctic water column stratification during episodes of minimum sea ice cover are sparse. The normal paleoceanographic proxies for water mass stratification cannot be applied in the Arctic; different approaches are required to reconstruct water column hydrography. The proposed research has the potential to greatly improve our knowledge of past Arctic water column hydrography from the early to mid-Holocene sea ice minimum and inform scenario development of future conditions in the Arctic Ocean.

The project will contribute to workforce development through support for the training of a PhD student. The technology developed will be proactively transferred to the international science community through a formal workshop.

Recent innovations in the combined use of secondary ion mass spectrometry (SIMS), laser-ablation inductively coupled plasma mass spectrometry (laser-ablation ICP-MS) and Isotope ratio mass spectrometry (IRMS) have shown that a wealth of environmental information about water column stratification can be extracted from single shells of fossil foraminifera. Neogloboquadrina pachyderma (sinistral) (Nps), grows its chambers (ontogenetic calcite) near the Arctic surface, and subsequently sinks through the water column where it adds a thick calcite crust around the thinly calcified chambers at sub-mixed layer depths. Thus, each individual Nps shell contains chemical and isotopic zonation from waters with distinctly different physical properties ? the generally cold low salinity surface mixed layer and warmer subsurface halocline. Intrashell variability can be measured with in situ analytical approaches. The principal investigators (PIs) propose to apply a multi-instrument approach to quantify intrashell geochemistry in Nps shells obtained from an array of boxcore samples across the Arctic Ocean. They plan to combine intrashell ä18O and ä13C measurements in