Variable habitat depth of the planktonic foraminifera <i>Neogloboquadrina pachyderma</i> in the northern high latitudes explained by sea-ice and chlorophyll concentration

Abstract

<p><strong>Abstract.</strong> Neogloboquadrina pachyderma is the dominant species in the polar regions. In the northern high latitude ocean, it makes up more than 90 % of the total planktonic foraminifera assemblages, making it the dominant pelagic calcifier and carrier of paleoceanographic proxies. To assess the reaction of this species to future climate change and to be able to interpret the paleoecological signal contained in its shells, its habitat depth must be known. Previous work showed that <i>N. pachyderma</i> in the northern polar regions has a highly variable depth habitat, ranging from the surface mixed layer to several hundreds of metres below the surface, and the origin of this variability remained unclear. In order to investigate the factors controlling the habitat depth of <i>N. pachyderma</i>, we compiled new and existing population density profiles from 104 stratified plankton tow hauls collected in the Arctic and the North Atlantic Oceans during 14 oceanographic expeditions. For each vertical profile, the Depth Habitat (DH) was calculated as the abundance-weighted mean depth of occurrence. We then tested to what degree environmental factors (mixed layer depth, sea surface temperature, sea surface salinity, Chlorophyll a concentration and sea ice concentration) and ecological factors (synchronised reproduction and daily vertical migration) can predict the observed DH variability and compared the observed DH behaviour with simulations by a numerical model predicting planktonic foraminifera distribution. Our data show that the DH of <i>N. pachyderma</i> varies between 25 m and 280 m (average ~ 100 m). In contrast with the model simulations, which indicate that DH is associated with the depth of chlorophyll maximum, our analysis indicates that the presence of sea-ice together with the concentration of chlorophyll at the surface have the strongest influence on the vertical habitat of this species. <i>N. pachyderma</i> occurs deeper when sea-ice and chlorophyll concentrations are low, suggesting a time transgressive response to the evolution of (near) surface conditions during the annual cycle. Since only surface parameters appear to affect the vertical habitat of <i>N. pachyderma</i>, light or light-dependant processes might influence the ecology of this species. Our results can be used to improve predictions of the response of the species to climate change and thus to refine paleoclimatic reconstructions.</p>

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

“…Yet our understanding of LPF ecology is fragmented, especially in the northern polar regions. Little is known about causes of interannual variability in production in terms of absolute abundance (concentration) and species distribution patterns (e.g., Schiebel, 2002;Schiebel & Hemleben, 2000), the controls of vertical habitat changes (Greco et al, 2019;Kretschmer et al, 2018;Rebotim et al, 2017), and how the vertical habitat varies ontogenetically (Bijma et al, 1990;Hemleben et al, 1989;Schiebel et al, 1997). Also, linkage between the reproduction cycle of the LPF and the lunar cycle is barely known (Bijma et al, 1990;Erez et al, 1991;Hemleben et al, 1989;Jonkers et al, 2015;Schiebel & Hemleben, 2017;Volkmann, 2000).…”

Insolation and Glacial Meltwater Influence on Sea‐Ice and Circulation Variability in the Northeastern Labrador Sea During the Last Glacial Period

“…In the following discussion we use some general characteristics for subdividing the studied period and interpreting the environmental conditions: As foraminifer production and flux in the polar region is highly influenced by food availability, an extensive sea‐ice cover in the polar region and its associated limited light penetration, is the primary influence leading to reduced fluxes (Carstens et al, ; Kohfeld et al, ; Ramseier et al, ). Hence, as light and nutrients are limited below sea‐ice, the foraminifer flux can be used as a proxy for sea‐ice cover changes (Greco et al, ). Oceanic frontal processes provide an increased nutrient supply and enhanced productivity although they are also linked to the extent of the summer (polar front) or winter (arctic front) sea‐ice cover (Johannessen et al, ).…”

“…Just before and after the H6 meltwater peak (GI‐18 and GI‐17), the 22CC foraminifer flux increases to moderate levels when the δ 18 O values increase, apparently as a result of diminished freshwater input. N. pachyderma is thought to adjust its depth habitat following the pycnocline and hence inhabits greater depths during conditions of increased freshwater supply or sea‐ice (Greco et al, ;Pflaumann et al, ; Simstich et al, ). We exclude the possibility of lower fluxes due to sediment export or erosion since we expect bottom currents to be weaker during this glacial period as the thermohaline circulation was also reduced during H6 (Böhm et al, ; Hunter, Wilkinson, Louarn, et al, ; Rahmstorf, ).…”

“…Although the habitat depth of N. pachyderma is quite variable and driven by sea‐ice and the concentration of chlorophyll (Greco et al, ), it is usually concentrated around an isopycnal layer with water densities between 27.7 and 27.8 (σ τ , Kozdon et al, ) at water depths between 70 and 130 m below the fresh EGC. However, depleted planktic δ 18 O values might indicate a conservative estimate of meltwater input (Simstich et al, ).…”

Amino acid racemization in Quaternary foraminifera from the Yermak Plateau

“…The Yermak Plateau, located north of the Svalbard archipelago, lies at the gateway to the central 85 Arctic Ocean, in an area characterized by the interaction between Atlantic and Arctic waters. The cold surface layer is dominated by the polar foraminifera N. pachyderma, which has highest abundances in the top 200 m (Carstens and Wefer, 1992;Carstens et al, 1997;Pados and Spielhagen, 2014;Greco et al, 2019). Cassidulina neoteretis is one of the dominant benthic species in sediments from the Yermak Plateau (Bergsten, 1994;Wollenburg and Mackensen, 1998;Wollenburg et al, 2004) and its abundance is often associated with the presence of Atlantic water (Polyak and 90 Solheim, 1994;Slubowska et al, 2005).…”