Particulate Organic Matter Distributions in the Water Column of the Chukchi Sea During Late Summer

Miguel A Goñi,Kylie A Welch,Rachel E Sipler,Lauren W Juranek

doi:10.1029/2021jc017664

Miguel A Goñi, Kylie A Welch + Show 2 more

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https://doi.org/10.1029/2021jc017664

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Abstract

AbstractTwo oceanographic cruises were completed in September 2016 and August 2017 to investigate the distribution of particulate organic matter (POM) across the northeast Chukchi Shelf. Both periods were characterized by highly stratified conditions, with major contrasts in the distribution of regional water masses that impacted POM distributions. Overall, surface waters were characterized by low chlorophyll fluorescence (Chl Fl < 0.8 mg m−3) and particle beam attenuation (cp < 0.3 m−1) values, and low concentrations of particulate organic carbon (POC < 8 mmol m−3), chlorophyll and pheophytin (Chl + Pheo < 0.8 mg m−3), and suspended particulate matter (SPM ∼2 g m−3). Elevated Chl Fl and Chl + Pheo (∼2 mg m−3) values measured at mid‐depths below the pycnocline defined the subsurface chlorophyll maxima (SCM), which exhibited moderate POC (∼10 mmol m−3), cp (∼0.4 m−1) and SPM (∼3 g m−3). In contrast, deeper waters below the pycnocline were characterized by low Chl Fl and Chl + Pheo (∼0.7 mg m−3), high cp (>1.5 m−1) and SPM (>8 g m−3) and elevated POC (>10 mmol m−3). POM compositions from surface and SCM regions of the water column were consistent with contributions from active phytoplankton sources whereas samples from bottom waters were characterized by high Pheo/(Chl + Pheo) ratios (>0.4) indicative of altered phytoplankton detritus. Marked contrasts in POM were observed in both surface and middepth waters during both cruises. Increases in chlorophyll and POC consistent with enhanced productivity were measured in middepth waters during the September 2016 cruise following a period of downwelling‐favorable winds, and in surface waters during the August 2017 cruise following a period of upwelling‐favorable winds.

Highlights

Surface warming associated with increased atmospheric CO2 concentrations is occurring in the Arctic at a pace roughly double the global average (e.g., Allen et al, 2018), leading to significant decreases in sea ice extent and thickness, and changes in the timing of seasonal melt and refreeze throughout the Arctic Ocean (e.g., Fetterer et al, 2017; Stroeve & Notz, 2018; Wood et al, 2015)
Two oceanographic cruises were completed in September 2016 and August 2017 to investigate the distribution of particulate organic matter (POM) across the northeast Chukchi Shelf
Surface waters were characterized by low chlorophyll fluorescence (Chl chlorophyll concentration based on fluorescence (Fl) < 0.8 mg m−3) and particle beam attenuation values, and low concentrations of particulate organic carbon (POC < 8 mmol m−3), chlorophyll and pheophytin (Chl + Pheo < 0.8 mg m−3), and suspended particulate matter (SPM ∼2 g m−3)

Summary

Introduction

Surface warming associated with increased atmospheric CO2 concentrations is occurring in the Arctic at a pace roughly double the global average (e.g., Allen et al, 2018), leading to significant decreases in sea ice extent and thickness, and changes in the timing of seasonal melt and refreeze throughout the Arctic Ocean (e.g., Fetterer et al, 2017; Stroeve & Notz, 2018; Wood et al, 2015). Remote-sensing based observations indicate increases in the extent and duration of the open water season over the past two decades have contributed to the enhancement in net primary production along Arctic marginal seas over this period (Arrigo & van Dijken, 2015; Lewis et al, 2020). Analyses by these authors suggest that the observed increases in net primary production over the past 10 years are driven by enhanced phytoplankton biomass, indicating that increases in nutrient supply are required to support the observed productivity increases. While the mean flow is from the Pacific to the Arctic, once inside the Chukchi Sea circulation is Figure 1

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