Upper-ocean flux of biogenic calcite produced by the Arctic planktonic foraminifera Neogloboquadrina pachyderma

[摘要] With ongoing warming and sea ice loss, the Arctic Oceanand its marginal seas as a habitat for pelagic calcifiers are changing,possibly resulting in modifications of the regional carbonate cycle and thecomposition of the seafloor sediment. A substantial part of the pelagiccarbonate production in the Arctic is due to the calcification of thedominant planktonic foraminifera species Neogloboquadrina pachyderma . To quantify carbonate productionand loss in the upper water layer by this important Arctic calcifier, wecompile and analyse data from vertical profiles in the upper water column ofshell number concentration, sizes and weights of this species acrossthe Arctic region during summer. Our data are inconclusive on whether thespecies performs ontogenetic vertical migration throughout its life cycle orwhether individual specimens calcify at a fixed depth within the verticalhabitat. The base of the productive zone of the species is on averagelocated below 100 m and at maximum at 300 m and is regionally highlyvariable. The calcite flux immediately below the productive zone (exportflux) is on average 8 mg CaCO 3  m −2  d −1 , and we observe thatthis flux is attenuated until at least 300 m below the base of theproductive zone by a mean rate of 6.6 % per 100 m. Regionally, the summerexport flux of N. pachyderma calcite varies by more than 2 orders of magnitude, and theestimated mean export flux below the twilight zone is sufficient to accountfor about a quarter of the total pelagic carbonate flux in the region. Theseresults indicate that estimates of the Arctic pelagic carbonate budget willhave to account for large regional differences in the export flux of themajor pelagic calcifiers and confirm that substantial attenuation of theexport flux occurs in the twilight zone.

[学科分类] 大气科学