Properties of Sediment Trap Catchment Areas in Fram Strait: Results From Lagrangian Modeling and Remote Sensing

Claudia Wekerle,Ian Salter,Tilman Dinter,Wilken-Jon Von Appen,Morten Hvitfeldt Iversen,Thomas Krumpen

doi:10.3389/fmars.2018.00407

Abstract

Vertical particle fluxes are responsible for the transport of carbon and biogenic material from the surface to the deep ocean, hence understanding these particle fluxes is of climate relevance. Sediment traps operated in Fram Strait in the framework of the Arctic long-term observatory FRAM provide an estimate of vertical particle fluxes in a region of high CO2 uptake. Until now the source area (catchment area) of trapped particles is unclear; however, lateral advection of particles is supposed to play an important role. This study presents a Lagrangian method to backtrack the origin of particles for two Fram Strait moorings equipped with sediment traps in 200 m and 2300 m depth by using the time-dependent velocity field of a high-resolution, eddy-resolving ocean-sea ice model. Our study shows that the extent of the catchment area is larger the deeper the trap and the slower the settling velocity. Chlorophyll-a concentration as well as sea ice coverage of the catchment area are highest in the summer months. The high sea ice coverage in summer compared to winter can possibly be related to a weaker across-strait sea level pressure difference, which allows more sea ice to enter the then well-stratified central Fram Strait where moorings are located. Hence, highest vertical particle fluxes may be expected in late summer and autumn. Furthermore, a backward sea ice tracking approach shows that the origin and age of sea ice drifting through Fram Strait, partly responsible for vertical particle fluxes, varies strongly from year to year, pointing to a high variability in the composition of particles trapped in the moorings.

Highlights

The oceans play a critical role in the global carbon cycle through regulating the exchange of carbon dioxide between atmospheric and oceanic reservoirs
In this study we developed a Lagrangian model to determine the catchment area of sediment traps attached to two moorings operated in central Fram Strait
The simulated catchment area of mooring HG-IV, which is located around 80 km south of HGN, is mostly characterized by Atlantic Water

Summary

Introduction

The oceans play a critical role in the global carbon cycle through regulating the exchange of carbon dioxide between atmospheric and oceanic reservoirs. The biological carbon pump is perhaps the most widely studied and traditionally refers to the gravitational settling of particles produced in the surface to the ocean interior (Sarmiento and Gruber, 2006) It is comprised of two components: the soft-tissue pump (Volk and Hoffert, 1985) and the carbonate counter pump (Heinze and Maier-Reimer, 1991). The carbonate counter pump is related to the precipitation of calcium carbonate minerals that act as a source of CO2 to the atmosphere over climatically-relevant timescales (Zeebe, 2012) The balance of these two processes governs the net sequestration of atmospheric CO2 into the ocean interior (Antia et al, 2001; Salter et al, 2014) and has an important impact on global climate (Sarmiento and Toggweiler, 1984; Sabine et al, 2004; Kwon et al, 2009). A good understanding of the mechanisms transferring biogenic particles from the surface to the deep-ocean and sediments is critical

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