Strategies for the Simulation of Sea Ice Organic Chemistry: Arctic Tests and Development

TL;DR

This paper develops and tests a reduced model simulating organic chemistry in Arctic sea ice, linking biogeochemical processes with physical ice dynamics to understand organic matter buildup.

Contribution

It introduces a novel integrated model connecting ice algal ecodynamics with organic macromolecule accumulation in sea ice brine channels.

Findings

Simulated chlorophyll maxima are consistent with observations but delayed.

Organic injection through cell disruption and exudation matches measured organic levels.

The model suggests high molecular weight organics influence ice matrix properties.

Abstract

A mechanism connecting ice algal ecodynamics with the buildup of organic macromolecules in brine channels is tested offline in a reduced model of pack geochemistry. Driver physical quantities are extracted from the global sea ice dynamics code CICE, including snow height, column thickness and internal temperature. The variables are averaged at the regional scale over ten Arctic biogeographic zones and treated as input matrices at four vertical habitat levels. Nutrient-light-salt limited ice algal growth is computed along with the associated grazing plus mortality. Vertical transport is diffusive but responds to pore structure. Simulated bottom layer chlorophyll maxima are reasonable, though delayed by about a month relative to observations. This highlights major uncertainties deriving from snow thickness variability. Upper level biota are generated intermittently through flooding. Macromolecular injections are represented by the compound classes humics, proteins, polysaccharides and lipids. The fresh biopolymers behave in a successional manner and are removed by bacteria. In baseline runs, organics are introduced solely through cell disruption, and internal carbon is biased low. Continuous exudation is therefore appended, and agreement with dissolved organic or individual biopolymer measurements is achieved when strong release is coupled to light availability. Detrital carbon then reaches hundreds of micromolar, sufficient to support physical changes to the ice matrix. Through this optimized model version we address the question, are high molecular weight organics added to the brine network over and above background spillage? The mechanism is configured for ready extension to the Antarctic, so that global ice organic chemistry issues can be targeted.