Sediment community biomass and respiration in the Northeast Water Polynya, Greenland: A numerical simulation of benthic lander and spade core data
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abstract
Sediment community metabolism (oxygen demand) was measured in the Northeast Water (NEW) polynya off Greenland employing two methods: in situ benthic chambers deployed with a benthic (GOMEX) lander and shipboard laboratory Batch Micro-Incubation Chambers (BMICs) utilizing 'cores' recovered from USNEL box cores. The mean benthic respiration rate measured with the lander was 0.057 mM O2 m-2 h-1 (n = 5); whereas the mean measured with the BMICs was 0.11 mM O2 m-2 h-1 (n = 21; p < 0.01 that the means were the same). In terms of carbon fluxes (14 and 27 mg C m-2 d-1), these respiration rates represent ca. 5-15% of the average net primary production measured in the euphotic zone in 1992. The biomass of the bacteria, meiofauna and macrofauna were measured at each location to quantify the relationship between total community respiration and total community biomass (mean 1.42 g C m-2). Average carbon residence time in the biota, calculated by dividing the biomass by the respiration, was on the order of 50-100 days, which is comparable to relatively oligotrophic continental margins at temperate latitudes. The biomass and respiration data for the aerobic heterotrophic bacteria, the infaunal invertebrates (meiofauna and macrofauna), and the epifaunal megabenthos (two species of brittle stars) are summarized in a 'steady state' solution of a sediment food chain model, in terms of carbon. This carbon budget illustrates the relative importance of the sediment-dwelling invertebrates in the benthic subsystem, compared to the bacteria and the epibenthos, during the summer open-water period in mud-lined troughs at depths of about 300 m. The input needed to drive heterotrophic respiratory processes was within the range of the input of organic matter recorded in moored, time sequencing sediment traps. A time-dependent numerical simulation of the model was run to investigate the potential responses of the three size groups of benthos to abrupt seasonal pulses of particulate organic matter. The model suggests that there is a time lag in the increase in bottom community biomass and respiration following the POC pulse, and provides hypothetical estimates for the potential carbon storage in the summer (open water), followed by catabolic losses during each ensuing winter (ice covered). This sequence of storage and respiration may contribute to the process of seasonal CO2 'rectification' (sensu Yager et al., 1995) in some Arctic ecosystems.
