Description: This is the ostracods census data from 157 sub-samples from two marine sediment cores, JM10-10GC and JM10-12GC, from Storfjorden, Svalbard. Cores were taken in October 2010 by RV 'Jan Mayen'. JM10-10GC is 402 cm long, sampled at 5-cm intervals. JM10-12GC is 320 cm long, sampled at 4-cm intervals. The cores comprise the last 13500 years. Cores were split in two halves and one half of each core was cut up in 1 cm thick sample slices. Each sample slice at 5 cm (core JM10-10GC) and 4 cm (cores JM10-12GC) interval was wet sieved with mesh sizes of 63, 100 and 1000 μm, oven dried, and then dry sieved with mesh-size of 150 μm. The size fraction 〉150 μm was analyzed for the content of benthic ostracods. All species were identified to species level.

Description: Aims Within the intensively‐studied, well‐documented latitudinal diversity gradient, the deep‐sea biodiversity of the present‐day Norwegian Sea stands out with its notably low diversity, constituting a steep latitudinal diversity gradient in the North Atlantic. The reason behind this has long been a topic of debate and speculation. Most prominently, it is explained by the deep‐sea glacial disturbance hypothesis, which states that harsh environmental glacial conditions negatively impacted Norwegian Sea diversities, which have not yet fully recovered. Our aim is to empirically test this hypothesis. Specific research questions are: (1) Has deep‐sea biodiversity been lower during glacials than during interglacials? ( 2) Was there any faunal shift at the Mid‐Brunhes Event (MBE) when the mode of glacial–interglacial climatic change was altered? Location Norwegian Sea, deep sea (1819–2800 m), coring sites MD992277, PS1243, and M23352. Time period 620.7–1.4 ka (Middle Pleistocene–Late Holocene). Taxa studied Ostracoda (Crustacea). Methods We empirically test the deep‐sea glacial disturbance hypothesis by investigating whether diversity in glacial periods is consistently lower than diversity in interglacial periods. Additionally, we apply comparative analyses to determine a potential faunal shift at the MBE, a Pleistocene event describing a fundamental shift in global climate. Results The deep Norwegian Sea diversity was not lower during glacial periods compared to interglacial periods. Holocene diversity was exceedingly lower than that of the last glacial period. Faunal composition changed substantially between pre‐ and post‐MBE. Main conclusions These results reject the glacial disturbance hypothesis, since the low glacial diversity is the important precondition here. The present‐day‐style deep Norwegian Sea ecosystem was established by the MBE, more specifically by MBE‐induced changes in global climate, which has led to more dynamic post‐MBE conditions. In a broader context, this implies that the MBE has played an important role in the establishment of the modern polar deep‐sea ecosystem and biodiversity in general.

Description: 〈jats:title〉Abstract〈/jats:title〉〈jats:sec〉〈jats:title〉Aim〈/jats:title〉〈jats:p〉Within the intensively‐studied, well‐documented latitudinal diversity gradient, the deep‐sea biodiversity of the present‐day Norwegian Sea stands out with its notably low diversity, constituting a steep latitudinal diversity gradient in the North Atlantic. The reason behind this has long been a topic of debate and speculation. Most prominently, it is explained by the deep‐sea glacial disturbance hypothesis, which states that harsh environmental glacial conditions negatively impacted Norwegian Sea diversities, which have not yet fully recovered. Our aim is to empirically test this hypothesis. Specific research questions are: (1) Has deep‐sea biodiversity been lower during glacials than during interglacials? 〈jats:italic〉(〈/jats:italic〉2) Was there any faunal shift at the Mid‐Brunhes Event (MBE) when the mode of glacial–interglacial climatic change was altered?〈/jats:p〉〈/jats:sec〉〈jats:sec〉〈jats:title〉Location〈/jats:title〉〈jats:p〉Norwegian Sea, deep sea (1819–2800 m), coring sites MD992277, PS1243, and M23352.〈/jats:p〉〈/jats:sec〉〈jats:sec〉〈jats:title〉Time period〈/jats:title〉〈jats:p〉620.7–1.4 ka (Middle Pleistocene–Late Holocene).〈/jats:p〉〈/jats:sec〉〈jats:sec〉〈jats:title〉Taxa studied〈/jats:title〉〈jats:p〉Ostracoda (Crustacea).〈/jats:p〉〈/jats:sec〉〈jats:sec〉〈jats:title〉Methods〈/jats:title〉〈jats:p〉We empirically test the deep‐sea glacial disturbance hypothesis by investigating whether diversity in glacial periods is consistently lower than diversity in interglacial periods. Additionally, we apply comparative analyses to determine a potential faunal shift at the MBE, a Pleistocene event describing a fundamental shift in global climate.〈/jats:p〉〈/jats:sec〉〈jats:sec〉〈jats:title〉Results〈/jats:title〉〈jats:p〉The deep Norwegian Sea diversity was not lower during glacial periods compared to interglacial periods. Holocene diversity was exceedingly lower than that of the last glacial period. Faunal composition changed substantially between pre‐ and post‐MBE.〈/jats:p〉〈/jats:sec〉〈jats:sec〉〈jats:title〉Main conclusions〈/jats:title〉〈jats:p〉These results reject the glacial disturbance hypothesis, since the low glacial diversity is the important precondition here. The present‐day‐style deep Norwegian Sea ecosystem was established by the MBE, more specifically by MBE‐induced changes in global climate, which has led to more dynamic post‐MBE conditions. In a broader context, this implies that the MBE has played an important role in the establishment of the modern polar deep‐sea ecosystem and biodiversity in general.〈/jats:p〉〈/jats:sec〉