Response of Recent Benthic Foraminiferal Assemblages to Contrasting Environments in Baffin Bay and the Northern Labrador Sea, Northwest Atlantic

Abstract

ABSTRACT. Modern deep-water benthic foraminiferal assemblages in Baffin Bay and the northern Labrador Sea, Western North Atlantic, were sampled from box cores and analyzed to determine assemblage composition. The two marine basins are separated by the shallow waters of Davis Strait. Assemblages of Baffin Bay contained only agglutinated foraminifera, whereas samples from the Labrador Sea contained both calcareous and agglutinated species, which resulted in significantly higher species richness. The absence of benthic calcareous taxa in Baffin Bay is attributed to cold, saline, CO 2 -rich bottom waters related to the Baffin Bay Bottom Water and the Baffin Bay Atlantic Water. Modern foraminiferal assemblage distribution supports the model of increased organic flux under seasonal open-water conditions that feed a rich agglutinated assemblage, but lead to oxidation of organic matter and increased carbonate dissolution. Deep-water sediments contain ice-rafted coarsegrained components and biogenic elements such as sponge spicules that are heavily used by numerous agglutinated species for test construction. Robust, tubular suspension feeders occupy regions under the influence of bottom currents that deliver nutrients. Although disturbances of the sediment-water interface cannot be excluded with sampled box cores, small-scale patchiness can be confirmed by varying abundances of infaunal taxa. Absolute counts of specimens in subsamples vary significantly, whereas species evenness among subsamples is less variable. These findings call for caution when interpreting lateral faunal changes on the basis of small core samples.Key words: benthic foraminifera, Baffin Bay, Labrador Sea, carbonate dissolution, faunal patchiness RÉSUMÉ. Nous avons échantillonné des assemblages modernes de foraminifères benthiques d'eau profonde prélevés dans la baie de Baffin et le nord de la mer du Labrador, Atlantique du Nord-Ouest, à partir de carottes à boîte, puis nous les avons analysés afin d'en déterminer la composition. Les deux bassins marins sont séparés par les eaux peu profondes du détroit de Davis. Les assemblages de la baie de Baffin ne renfermaient que des foraminifères agglutinants, tandis que les échantillons de la mer du Labrador contenaient à la fois des espèces calcaires et des espèces agglutinantes, ce qui a donné lieu à une richesse d'espèces considérablement supérieure. L'absence de taxons calcaires benthiques dans la baie de Baffin s'explique par la présence d'eau de fond froide, saline et riche en CO 2 provenant de l'eau de fond de la baie de Baffin et de l'eau atlantique de la baie de Baffin. La répartition des assemblages foraminifères modernes cadre avec le modèle du flux organique accru moyennant des conditions saisonnières en eaux libres qui alimentent un riche assemblage agglutinant, mais qui se traduisent par l'oxydation de la matière organique et l'intensification de la dissolution du carbonate. Les sédiments en eau profonde contiennent des composantes glacielles à grains grossiers et des éléments biogènes tels que ...

A micropalaeontological perspective on export productivity, oxygenation and temperature in NE Atlantic deep-waters across Terminations I and II

“…A severe decrease in the abundance of agglutinated shells apparently occurs within the first 20 cm below the mudline, and their contribution to the fossil assemblages never exceeds 16% and remains < 5% in most of the samples studied. A similar decline within the first 10-20 centimeters of deep-sea sediments has been reported from other sites and attributed to selective preservation of hard-shelled carbonate over soft-shelled agglutinated foraminiferal shells (Schröder, 1988;Kuhnt et al, 2000;Schröder-Adams and van Rooyen, 2011;Lejzerowicz et al, 2013). Strong indications that the decline of agglutinated shells at U1385 is a taphonomic rather than a biological signal arise from two observations.…”

Palaeoceanographic development in Storfjorden, Svalbard, during the deglaciation and Holocene: evidence from benthic foraminiferal records

“…Today, these four species are characteristic constituents of faunas in the inner fjords of Spitsbergen, especially in areas affected by freshwater runoff (see above). They also occur in Baffin Bay, where they are found in the cold corrosive, deep water below the CCD in areas with seasonal sea ice cover and high food supply ( R. turbinatus is here recorded as R. contortus ; Schröder‐Adams & van Rooyen ). Recurvoides turbinatus and R. scorpiurus are characterized as winter species similar to S. loeblichi (Korsun & Hald ).…”

“…). In Baffin Bay, A. glomerata seems to prefer the cold water below the carbonate compensation depth (CCD) in areas with seasonal sea ice cover and high productivity (Schröder‐Adams & van Rooyen ). It is characterized as an epifaunal to shallow infaunal species.…”

“…They are the most important species in Lancaster Sound and Baffin Bay in areas with seasonal sea ice cover (Schröder‐Adams et al . ; Schröder‐Adams & van Rooyen ), and according to Wollenburg & Mackensen () and Wollenburg & Kuhnt () they occur widely distributed in the Arctic Ocean in areas with seasonal sea ice cover.…”

Water mass exchange between the Nordic seas and the Arctic Ocean on millennial timescale during MIS 4–MIS 2

“…[], Hald and Steinsund [], and Saher et al . [] and samples from the warmer realm using published records from Ireland, Bay of Biscay, off Portugal, the central North Atlantic Ocean, the east coast of Canada, and the United States [ Seiler , ; Schafer and Cole , ; Hermelin and Scott , ; Weston , ; Corliss , ; Austin and Evans , ; Fontanier et al ., ; Schönfeld , ; Sun et al ., ; Margreth et al ., ; Mojtahid et al ., ; Duros et al ., ; Schröder‐Adams and van Rooyen , ].…”