Antarctic sea ice greatly impacts the Southern Ocean’s biogeochemical cycles and ecosystem dynamics by providing a unique habitat through its intricate brine channels and pockets, known as the sympagic sea ice community. This community, abundant in diverse biota, plays a critical ecological role in the region. However, faunal components like microzooplankton, including foraminifera such as Neogloboquadrina pachyderma have been understudied despite their prevalence in contemporary high-latitude planktonic communities and Southern Ocean sediment samples. During the ANT29-7 expedition aboard the RV Polarstern from August 14 to October 13, 2013, ice cores were collected from three dive transects (EB, POL, ROV) on an ice floe at 60°47.76’S and 26°19.73’W in the Weddell Sea. Sampling involved obtaining three replicate ice cores at 2-meter intervals along each transect. The ice cores (each 100 cm long) were analyzed in two sections: the lower 0-10 cm representing the seawater-ice interface and the upper 10-100 cm. Planktonic foraminifera were studied quantitatively and qualitatively, focusing on density (n°/l) and biomass (μgrC/l) across three size fractions (> 150; 150-63; and 63-10 μm). The most common size fraction in both upper and lower sea-ice samples was between 63 and 150 μm. Density ranged from 2.8 n°/l to 97.2 n°/l in upper sea-ice and from 1.9 n°/l to 329.6 n°/l in lower sea-ice across all size fractions. Biomass values followed a similar trend, ranging from 0.4 μgrC/l to 8.9 μgrC/l in upper sea-ice and from 1.0 μgrC/l to 25.9 μgrC/l in lower sea-ice. Planktonic foraminifera were predominantly found at the seawater-ice interface (756 n°/l upper sea-ice vs 1140 n°/l lower sea-ice), consistent with previous Weddell Sea studies where foraminiferal numbers ranged from 87 to 1075 n°/l, mainly in the lower sea-ice core portion with sizes under 100 μm. All planktonic foraminifera identified belonged to the Neogloboquadrina pachyderma species. Quantitative and qualitative morphometric analyses differentiate individuals from the water column and sea ice, although with some overlap. Sea ice specimens are typically larger, always have a lip at the aperture, and exhibit more morphological variation compared to those from seawater. Linear Discriminant Analysis (LDA) using Fourier shape analysis effectively distinguishes between these groups with minimal overlap. These findings suggest the presence of a distinct type of N. pachyderma in sea-ice, characterized by unique shell features and adaptation to extreme temperature and salinity conditions. Further ultrastructural and genetic analyses are essential to confirm the presence of a sympagic species of planktonic foraminifera in sea-ice, providing valuable insights for paleoenvironmental reconstructions and paleoceanographic studies.
Assessing planktonic foraminiferal species from Antarctic sea-ice as a paleoceanographic proxy: preliminary insights.
Morigi C.Secondo
;
2024-01-01
Abstract
Antarctic sea ice greatly impacts the Southern Ocean’s biogeochemical cycles and ecosystem dynamics by providing a unique habitat through its intricate brine channels and pockets, known as the sympagic sea ice community. This community, abundant in diverse biota, plays a critical ecological role in the region. However, faunal components like microzooplankton, including foraminifera such as Neogloboquadrina pachyderma have been understudied despite their prevalence in contemporary high-latitude planktonic communities and Southern Ocean sediment samples. During the ANT29-7 expedition aboard the RV Polarstern from August 14 to October 13, 2013, ice cores were collected from three dive transects (EB, POL, ROV) on an ice floe at 60°47.76’S and 26°19.73’W in the Weddell Sea. Sampling involved obtaining three replicate ice cores at 2-meter intervals along each transect. The ice cores (each 100 cm long) were analyzed in two sections: the lower 0-10 cm representing the seawater-ice interface and the upper 10-100 cm. Planktonic foraminifera were studied quantitatively and qualitatively, focusing on density (n°/l) and biomass (μgrC/l) across three size fractions (> 150; 150-63; and 63-10 μm). The most common size fraction in both upper and lower sea-ice samples was between 63 and 150 μm. Density ranged from 2.8 n°/l to 97.2 n°/l in upper sea-ice and from 1.9 n°/l to 329.6 n°/l in lower sea-ice across all size fractions. Biomass values followed a similar trend, ranging from 0.4 μgrC/l to 8.9 μgrC/l in upper sea-ice and from 1.0 μgrC/l to 25.9 μgrC/l in lower sea-ice. Planktonic foraminifera were predominantly found at the seawater-ice interface (756 n°/l upper sea-ice vs 1140 n°/l lower sea-ice), consistent with previous Weddell Sea studies where foraminiferal numbers ranged from 87 to 1075 n°/l, mainly in the lower sea-ice core portion with sizes under 100 μm. All planktonic foraminifera identified belonged to the Neogloboquadrina pachyderma species. Quantitative and qualitative morphometric analyses differentiate individuals from the water column and sea ice, although with some overlap. Sea ice specimens are typically larger, always have a lip at the aperture, and exhibit more morphological variation compared to those from seawater. Linear Discriminant Analysis (LDA) using Fourier shape analysis effectively distinguishes between these groups with minimal overlap. These findings suggest the presence of a distinct type of N. pachyderma in sea-ice, characterized by unique shell features and adaptation to extreme temperature and salinity conditions. Further ultrastructural and genetic analyses are essential to confirm the presence of a sympagic species of planktonic foraminifera in sea-ice, providing valuable insights for paleoenvironmental reconstructions and paleoceanographic studies.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
