Estimates of net community production from multiple approaches surrounding the spring ice-edge bloom in Baffin Bay

Abstract

Measurements of net community production (NCP) provide an upper constraint on the strength of the oceanic biological pump, the dominant mechanism for removing CO2 from the ocean surface and sequestering it at depth. In this investigation, our objectives were to describe the spatial and temporal variability of NCP associated with the spring ice-edge bloom in Baffin Bay and to identify the key environmental drivers controlling its variability. Using data collected between June 9 and July 10, 2016, we estimated NCP based on (1) underway measurements of surface water oxygen to argon ratios (O2:Ar), (2) underway measurements of the partial pressure of CO2, and (3) seasonal nitrate drawdown from discrete samples. These multiple approaches displayed high NCP (up to 5.7 mol C m–2) in eastern Baffin Bay, associated with modified Atlantic waters, and low NCP (<1 mol C m–2) in the presence of Arctic outflow waters in western Baffin Bay. Arctic outflow waters were characterized by low surface salinities and nitrate concentrations, suggesting that high freshwater content may have limited the nutrient availability of these waters. Different integration depths and timescales associated with each NCP approach were exploited to understand the temporal progression and succession of the bloom, revealing that the bloom was initiated under ice up to 15 days prior to ice retreat and that a large portion of NCP in eastern Baffin Bay (potentially up to 70%) was driven by primary production occurring below the surface-mixed layer.

Sea ice concentration impacts dissolved organic gases in the Canadian Arctic

“…Higher concentrations near the surface at stations of low ice coverage appear to be consistent with a biological source of methanol in seawater as ice-free areas typically display higher net community production (Burgers et al, 2020) and most primary productivity tends to occur within the 30 m near the surface (Arrigo et al, 2011). We observe no obvious relationship between methanol concentration and Chl a in this dataset.…”

“…There are episodes of remarkably high acetaldehyde concentrations (around 10 nmol dm -3 ) during this cruise track. High biological (Burgers et al, 2020) and photochemical activity Ratte et al, 1998) combined with 24 h daylight might have led to strong production of acetaldehyde during some periods of our study.…”

“…10 m depth, Figure 7), similar to previous observations (Martin et al, 2010). This deep Chl a maximum at some of the stations (Figure 7) is characterised by very high levels of biological activity (Ardyna et al, 2013;Barber et al, 2015;Burgers et al, 2020).…”

“…If light dependent biological production of acetone were an important process in the sea ice zone, we would have expected to detect substantial acetone concentrations near depths of peak Chl a and down to the penetration depth of visible light (≈ 40 -50 m (Massicotte et al, 2018), Figure 7)) required for biological activity. In Baffin Bay area, potentially up to 70 % of the primary productivity is occurring at the deep Chl a maximum (Burgers et al, 2020). Earlier incubation experiments suggest that biological production of acetone is negligible (Dixon et al, 2013), while more recent field campaigns (Schlundt et al, 2017) and culture experiments (Halsey et al, 2017) suggest that acetone may have a considerable biological source.…”

Exploring Five Methods for Estimating Net Community Production on the Siberian Continental Shelf and Slope of the Arctic Ocean

“…One often-used method of calculating NCP involves estimating the seasonal drawdown of nutrients, typically nitrate, by comparing vertical profiles collected in a study area during winter/pre-bloom and summer/post-bloom (e.g., Macdonald et al, 1987;Anderson et al, 2003;Codispoti et al, 2013;Uflsbo et al, 2014;Burgers et al, 2020). For example, Codispoti et al (2013) compiled bottle nutrient data to apply this method and map NCP over pre-defined subregions across the Arctic Ocean.…”