Impacts of Basal Melting of the Totten Ice Shelf and Biological Productivity on Marine Biogeochemical Components in Sabrina Coast, East Antarctica

Abstract

To clarify the impacts of basal melting of the Antarctic ice sheet and biological productivity on biogeochemical processes in Antarctic coastal waters, concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA), inorganic nutrients, chlorophyll a, and stable oxygen isotopic ratios (δ18O) were measured from the offshore slope to the ice front of the Totten Ice Shelf (TIS) during the spring/summer of 2018, 2019, and 2020. Modified Circumpolar Deep Water (mCDW) intruded onto the continental shelf off the TIS and flowed along bathymetric troughs into the TIS cavity, where it formed a buoyant mixture with glacial meltwater from the ice shelf base. Physical oceanographic processes mostly determined the distributions of DIC, TA, and nutrient concentrations. However, photosynthesis and dilution by meltwater from sea ice and the ice shelf base decreased DIC, TA, and nutrient concentrations in surface water near the ice front. These causes also reduced the CO2 partial pressure in surface water by more than 100 μatm with respect to mCDW in austral summer of 2018 and 2020, and the surface water became a strong CO2 sink for the atmosphere. Phytoplankton photosynthesis changed DIC and TA in a molar ratio of 106:16. Thus, CO2 partial pressure decreased mostly as a result of photosynthesis while dilution by glacial and sea ice meltwater had a small effect. The nutrient consumption ratio suggested that photosynthesis was stimulated by iron in the water column, supplied to the surface layer via buoyancy‐driven upwelling and basal ice shelf meltwater in addition to sea ice meltwater.

Subglacial Freshwater Drainage Increases Simulated Basal Melt of the Totten Ice Shelf

“…Observations of this region suggest that it is undergoing ice surface lowering, retreat and mass loss (e.g., Flament & Rémy, 2012; Li et al., 2015; Pritchard et al., 2012; Roberts et al., 2018; Velicogna et al., 2020), although complex variability (Adusumilli et al., 2020; Gwyther et al., 2018) limits the ability to detect and attribute recent change. The observed oceanographic regime (Greene, Blankenship, et al., 2017; Rintoul et al., 2016; Silvano et al., 2017, 2019; T. P. Tamura et al., 2022; Williams et al., 2011) and bathymetric connections (e.g., Greenbaum et al., 2015) beneath and adjacent to the TIS indicate the potential for warm, off‐shelf waters to access the cavity and drive strong basal melting.…”

Quantitative Assessment of Factors Contributing to Variations in Sea Surface pCO2 in the Pacific Sector of the Arctic Ocean

“…The seasonal variation in DIC from winter to summer due to biological effects (Δ[ n DIC] winter–summer; that is., net community production) can be calculated from the change in nutrient content from winter to summer (e.g., Shadwick et al., 2014; Tamura et al., 2022). $$${\Delta }{[\text{DIC}]}_{\text{winter}\mbox{-}\text{summer}}=\left({[\mathit{nN}]}_{\text{TML}}\,-\,{[\mathit{nN}]}_{\text{surface}})\cdot (106/16\right)$$$ where [ nN ] TML is the nitrate content in the water TML and [ nN ] surface is the observed nitrate content normalized by the salinity in winter.…”

“…The seasonal variation in DIC from winter to summer due to biological effects (Δ[nDIC] winter-summer; that is., net community production) can be calculated from the change in nutrient content from winter to summer (e.g., Shadwick et al, 2014;Tamura et al, 2022).…”