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Controls on CO2 Fluxes in the Marginal Ice Zone: Biological Productivity and Air-Sea Gas Exchange

Rachel Stanley Brown, Marine Chemistry & Geochemistry
Brise Loose, Marine Chemistry & Geochemistry

Arctic Research Initiative
2010 Funded Project

Abstract

Polar ice zones are important regions for air-sea CO2 fluxes. However, CO2 fluxes in the ice zones have been hard to quantify, in large part because of the complicated physical and biological processes that take place during the spring bloom associated with ice melting. During the winter, sea ice acts as a barrier to air-sea gas exchange. In the spring, when the ice melts, biological production thrives as light and nutrients become plentiful. Quantifying biological production associated with ice melt, and its effect on CO2 fluxes, has proven difficult. Satellite algorithms are not effective due to the small spatial scale of productivity associated with leads in the ice. We propose to develop a new methodology for simultaneously quantifying biological production and air-sea gas exchange in melting ice zones.  We will use this methodology to study the interaction between ice melt, biological production, and gas exchange in a pilot study in the Bras D’Or Lakes, Nova Scotia.  The lakes, an analog to the Arctic environment, provide an ideal “natural” laboratory for studying ice melting processes in an easily-accessible, fully supported field environment. This study will serve as a logical first step towards applying this methodology in the Arctic.

Net community production (NCP) is the net amount of CO2 removed from the atmosphere by organisms and thus is of direct climatic relevance. We will quantify NCP on sub-kilometer scale resolution in the melting ice zone by using a field-capable mass spectrometer to measure oxygen and argon ratios. Additionally, we will quantify gross primary production (GPP), the base of the food chain, by using a novel gas tracer, the triple isotopic composition of oxygen. Concurrent measurements of NCP and GPP will allow us to quantify the recycling rate of the carbon. We will simultaneously quantify air sea gas exchange by making near real-time measurements of the gas tracer SF6.  The combination of measurements of two types of biological production and air-sea gas exchange made concurrently will provide mechanistic insights on the effect of melting sea ice on the carbon biological pump and CO2 fluxes. This study addresses the first key question of the ARI program – namely, the effects of changing sea ice cover on the Arctic carbon cycle.

Last updated: September 6, 2012