Planktic Foraminiferal and Pteropod Contributions to Carbon Dynamics in the Arctic Ocean (North Svalbard Margin)

Abstract

Planktic foraminifera and shelled pteropods are some of the major producers of calcium carbonate (CaCO3) in the ocean. Their calcitic (foraminifera) and aragonitic (pteropods) shells are particularly sensitive to changes in the carbonate chemistry and play an important role for the inorganic and organic carbon pump of the ocean. Here, we have studied the abundance distribution of planktic foraminifera and pteropods (individuals m–3) and their contribution to the inorganic and organic carbon standing stocks (μg m–3) and export production (mg m–2 day–1) along a longitudinal transect north of Svalbard at 81° N, 22–32° E, in the Arctic Ocean. This transect, sampled in September 2018 consists of seven stations covering different oceanographic regimes, from the shelf to the slope and into the deep Nansen Basin. The sea surface temperature ranged between 1 and 5°C in the upper 300 m. Conditions were supersaturated with respect to CaCO3 (Ω > 1 for both calcite and aragonite). The abundance of planktic foraminifera ranged from 2.3 to 52.6 ind m–3 and pteropods from 0.1 to 21.3 ind m–3. The planktic foraminiferal population was composed mainly of the polar species Neogloboquadrina pachyderma (55.9%) and the subpolar species Turborotalita quinqueloba (21.7%), Neogloboquadrina incompta (13.5%) and Globigerina bulloides (5.2%). The pteropod population was dominated by the polar species Limacina helicina (99.6%). The rather high abundance of subpolar foraminiferal species is likely connected to the West Spitsbergen Current bringing warm Atlantic water to the study area. Pteropods dominated at the surface and subsurface. Below 100 m water depth, foraminifera predominated. Pteropods contribute 66–96% to the inorganic carbon standing stocks compared to 4–34% by the planktic foraminifera. The inorganic export production of planktic foraminifera and pteropods together exceeds their organic contribution by a factor of 3. The overall predominance of pteropods over foraminifera in this high Arctic region during the sampling period suggest that inorganic standing stocks and export production of biogenic carbonate would be reduced under the effects of ocean acidification.

Upper-ocean flux of biogenic calcite produced by the Arctic planktonic foraminifera Neogloboquadrina pachyderma

“…For this comparison, we subdivided the regions by longitude to account for the different influences of Atlantic and Arctic waters, which play an important role for the abundances and habitats of planktonic foraminifera in this region (Pados and Spielhagen, 2014). The contribution of 10 % of planktonic foraminifera CaCO 3 fluxes to total CaCO 3 fluxes in the Fram Strait is in line with the lower end of the estimated contribution of planktonic foraminifera to total CaCO 3 fluxes at the northern Svalbard margin (4 %-34 %; Anglada-Ortiz et al, 2021). The higher contribution of planktonic foraminifera CaCO 3 fluxes to total CaCO 3 fluxes in the Greenland Sea is in the range of the estimates from Salter et al (2014) from the Crozet Plateau in the southern Indian Ocean, indicating that it falls within globally realistic ranges.…”

“…Taking all possible biases in our flux estimation, as well as effects on the flux from Schiebel (2002), into account, our estimates cannot be considered as substantially deviating from his flux estimates for the North Atlantic. An opportunity to further validate our calcite flux estimates is given by a recent study from the northern Svalbard margin by Anglada-Ortiz et al (2021), who reported total foraminifera calcite fluxes of 2.3 to 7.9 mg CaCO 3 m −2 d −1 based on data from living planktonic foraminifera in the upper 100 m of the water column. It has to be considered that this might not represent the export flux zone, as at least two of the studied profiles show increasing shell abundance below 100 m. Nevertheless, considering that the planktonic foraminifera assemblages reported by those authors contained only about 50 % N. pachyderma, their minimum reported flux is similar to the range of the estimates in our dataset for the Barents Sea at 100 m (0.39 to 1.86 mg CaCO 3 m −2 d −1 using different weight averages for the calculation).…”

“…Their contribution is likely even higher in the high-latitude oceans, where the main pelagic calcite producers, the Coccolithophoridae, are less abundant (Baumann et al, 2000;Daniels et al, 2016). For example, at the northern Svalbard margin, summertime calcite fluxes inferred from standing stocks of planktonic foraminifera at 100 m depth form about 4 %-34 % of total CaCO 3 fluxes in that area (Anglada-Ortiz et al, 2021).…”

“…The dominant planktonic foraminifera species in the Arctic Ocean is Neogloboquadrina pachyderma (Carstens et al, 1997;Volkmann, 2000b;Schiebel et al, 2017;Anglada-Ortiz et al, 2021). Like all extant planktonic foraminifera, the species builds its shell by sequential addition of increasingly larger chambers such that the largest amount of calcification occurs during the final stages of its life.…”

Decadal trend of plankton community change and habitat shoaling in the Arctic gateway recorded by planktonic foraminifera

“…Indeed, in the adjacent Barents Sea, in the absence of sea-ice export, the Atlantification of the foraminiferal community appears stronger (Ofstad et al, 2020), likely further enhanced by import of nutrients that promotes phytoplankton production (Lewis et al, 2020). This means that once the ice export in the Fram Strait ceases to be fuelled by the increasing Arctic sea-ice reduction (Årthun et al, 2021;Guarino et al, 2020), the planktonic community will likely abruptly shift to a completely different state with more Atlantic and more non-sea-ice species, possibly impacting the carbon export of the region (Anglada-Ortiz et al, 2021). Observational data of sea-ice extent and future predictions plotted in Figure 1d show that, in the Fram Strait, the trend towards an increase in sea-ice export seems to have already reached its maximum.…”