Oxygen and carbon isotope composition of modern planktic foraminifera and near-surface waters in the Fram Strait (Arctic Ocean) – a case study

Abstract

Abstract. The upper 500 m of the water column and the sediment surface along an E-W transect in the Fram Strait were sampled for recent planktic foraminifera. The δ 18 O and δ 13 C values of the tests are compared to the stable isotope composition of the water samples taken from the same depths, and related to the characteristics of the water column. The polar species Neogloboquadrina pachyderma clearly dominates the species assemblage in the Fram Strait in the early summer, while the subpolar Turborotalita quinqueloba accounts only for 5-23 %. In this area the average depth of calcification of N. pachyderma lies between 70-150 m water depth, T. quinqueloba shows a similar range with 50-120 m water depth. The δ 18 O values of N. pachyderma show an average vital effect of about −1.5 ‰ compared to calculated equilibrium calcite values. Except for the upper ∼ 75 m, the vertical profiles of δ 13 C of the net-sampled shells are nearly parallel to the values measured in the water column with an average offset of −1.6 ‰ and −3.6 ‰ for N. pachyderma and T. quinqueloba, respectively. The discrepancy found in the upper ∼ 75 m might indicate an influence of the "carbonate ion effect" on the carbon isotope incorporation in the tests. Oxygen and carbon isotopes from the sediment surface yield higher values than those from the water column for both species. This may be because specimens from the water column reflect a modern snapshot only, while tests from surface sediments record environmental parameters from the past ∼ 1000 years.

Environmental variability off NE Greenland (western Fram Strait) during the past 10,600 years

“…Figure 1) which has relatively high δ 13 C values (cf. Pados et al, 2015). We note that the change from relatively high (~30%) to low (<20%) fragmentation around 8 ka in our core is opposite to what is observed in the deep Fram Strait (cf.…”

“…The δ 13 C values of planktic N. pachyderma were low in the Early Holocene part of our record (Figure 4a). Today, δ 13 C values of dissolved inorganic carbon (DIC) in western Fram Strait waters are highest in the upper 100 m (Pados et al, 2015). Further, a recent synoptic study revealed sea-ice coverage and the depth of the chlorophyll maximum as the major factors determining the vertical habitat of this species (Greco et al, 2019).…”

Development, Productivity, and Seasonality of Living Planktonic Foraminiferal Faunas and Limacina helicina in an Area of Intense Methane Seepage in the Barents Sea

“…The δ 13 C values of N. pachyderma and T. quinqueloba in the water column in June do not show anomalously negative values, indicating no incorporation of CH 4 -derived carbon in their tests. Both δ 13 C and δ 18 O values of N. pachyderma and T. quinqueloba are comparable to those reported in the Fram Strait (Pados et al, 2015) 10.1029/2019JG005387…”

The last two millennia: climate, ocean circulation and palaeoproductivity inferred from planktic foraminifera, south-western Svalbard margin

“…0 m). Neogloboquadrina pachyderma and N. incompta, which in Fram Strait prefer mainly Atlantic Water, are interpreted as indicators of subsurface water conditions and productivity at depths of about 250-75 m (e.g., Bé & Tolderlund 1971;Johannessen et al 1994;Volkmann & Mensch 2001;Simstich et al 2003;Pados & Spielhagen 2014;Pados et al 2015;Sarnthein & Werner 2017). Furthermore, we associate the SST TF estimated for 10-m water depth and the SST Mg/Ca based on N. pachyderma with surface and subsurface water temperatures, respectively.…”