Threatened species drive the strength of the carbonate pump in the northern Scotia Sea

Abstract

The efficiency of deep-ocean CO2 sequestration is regulated by the relative balance between inorganic and organic carbon export respectively acting through the biological carbon pump (BCP) and the carbonate counter pump (CCP). The composition and abundance of calcifying species in the prevailing oceanic plankton community plays a major role in driving the CCP. Here we assess the role of these calcifying organisms in regulating the strength of the CCP in a Southern Ocean region (northern Scotia Sea) known to be a major hotspot for the drawdown of atmospheric CO2. We show that, when shelled pteropods dominate the calcifying community, the total annual reduction of CO2 transferred to the deep ocean doubles (17%) compared to when other plankton calcifiers dominate (3–9%). Furthermore, predation enhances their contribution through the removal of organic soft tissue. Pteropods are threatened in polar regions by ocean warming and acidification. We determine that their potential decline would have major implications to the comparative strengths of the BCP and CCP.

Particle Fluxes at the Australian Southern Ocean Time Series (SOTS) Achieve Organic Carbon Sequestration at Rates Close to the Global Median, Are Dominated by Biogenic Carbonates, and Show No Temporal Trends Over 20-Years

“…Biogenic calcium carbonate is precipitated by calcifiers, most prominently foraminifera and coccolithophores, along with other zooplankton such as pteropods. The PIC fluxes allow us to address the opposing role of calcium carbonate as ballast to enhance particle sinking and thus the BCP versus alkalinity loss through production of CO 2 during calcium carbonate precipitation, which reduces CO 2 solubility and thus weakens the ocean CO 2 sink (known colloquially as the carbonate counter-pump, e.g., Rost and Riebesell, 2004;Manno et al, 2018). The BSi fluxes provide a gauge on the importance of diatoms, a phytoplankton functional group that forms silica frustules and has the ability to rapidly bloom and achieve high biomass and thus mediate strong export from the surface ocean (e.g., Dugdale et al, 1995).…”

Current and future ocean chemistry negatively impacts calcification in predatory planktonic snails

“…Calcifying planktonic gastropods play an important role in ocean carbonate flux, by transporting inorganic carbon from the ocean surface into deep waters via the rapid sinking of their relatively heavy calcium carbonate shells [1][2][3] . Although small (up to ~2 cm), holoplanktonic gastropods are widespread and can be highly abundant in the upper ocean, exceeding densities of 10,000 individuals per m 3 of seawater 4 .…”

Can lipid removal affect interpretation of resource partitioning from stable isotopes in Southern Ocean pteropods?

“…Few studies have employed SIA with Southern Ocean pteropods and, among them, fewer have accounted for lipids, making between‐study comparisons problematic. Given the essential roles of pteropods in contributing to deep sea CO 2 sequestration, and providing top‐down control on phytoplankton and smaller zooplankton concentrations, there is an urgent need to perform climate impact assessments on a relatively understudied organism highly sensitive to changes in ocean temperature and chemistry . We hypothesize that lipid extraction will result in a statistically significant increase in δ 13 C values relative to values from untreated samples that will consequently lead to significantly different outcomes in isotopic niche estimations.…”