Sea ice dynamics across the Mid-Pleistocene transition in the Bering Sea.

Sea ice and associated feedback mechanisms play an important role for both long- and short-term climate change. Our ability to predict future sea ice extent, however, hinges on a greater understanding of past sea ice dynamics. Here we investigate sea ice changes in the eastern Bering Sea prior to, across, and after the Mid-Pleistocene transition (MPT). The sea ice record, based on the Arctic sea ice biomarker IP25 and related open water proxies from the International Ocean Discovery Program Site U1343, shows a substantial increase in sea ice extent across the MPT. The occurrence of late-glacial/deglacial sea ice maxima are consistent with sea ice/land ice hysteresis and land-glacier retreat via the temperature-precipitation feedback. We also identify interactions of sea ice with phytoplankton growth and ocean circulation patterns, which have important implications for glacial North Pacific Intermediate Water formation and potentially North Pacific abyssal carbon storage

Impact of Geoid Improvement on Ocean Mass and Heat Transport Estimates.

International audienceOne long-standing difficulty in estimating the large-scale ocean circulation is the inability to observe absolute current velocities. Both conventional hydrographic measurements and altimetric measurements provide observations of currents relative to an unknown velocity at a reference depth in the case of hydrographic data, and relative to mean currents calculated over some averaging period in the case of altimetric data. Space gravity missions together with altimetric observations have the potential to overcome this difficulty by providing absolute estimates of the velocity of surface oceanic currents. The absolute surface velocity estimates will in turn provide the reference level velocities that are necessary to compute absolute velocities at any depth level from hydrographic data. Several studies have been carried out to quantify the improvements expected from ongoing and future space gravity missions. The results of these studies in terms of volume flux estimates (transport of water masses) and heat flux estimates (transport of heat by the ocean) are reviewed in this paper. The studies are based on ocean inverse modeling techniques that derive impact estimates solely from the geoid error budgets of forthcoming space gravity missions. Despite some differences in the assumptions made, the inverse modeling calculations all point to significant improvements in estimates of oceanic fluxes. These improvements, measured in terms of reductions of uncertainties, are expected to be as large as a factor of 2. New developments in autonomous ocean observing systems will complement the developments expected from space gravity missions. The synergies of in situ and satellite observing systems are considered in the conclusion of this paper

Occurrence of the autofluorescent pigment lipofuscin in polar crustaceans and its potential as age marker

The lack of reliable methods for age determination often complicates the determination of individual age which is a fundamental parameter for estimating growth in population dynamics. In crustaceans, the quantification of the autofluorescent age pigment lipofuscin has recently revealed more promising results in boreal and tropical species than traditional methods. The presence of morphological lipofuscin and its possible application as an age marker in polar species was assessed in brain sections of five Arctic and five Antarctic species comprising decapods, amphipods and a euphausiid. Lipofuscin granules were located using confocal fluorescence microscopy and quantified (as % lipofuscin area fraction) from digital images. The pigment was found in 94 of 100 individuals and in all ten species, and granules occurred in easily detectable amounts in five species. Two scavenging amphipod species, the Antarctic Waldeckia obesa and the Arctic Eurythenes gryllus, revealed the most conspicuous and numerous granules. There was a broad, though weak, correlation with individual body size within a species, but not with absolute body size of one species compared to another. In larvae of the decapod Chorismus antarcticus, lipofuscin accumulation was quantified over the first four months after larval release. Factors potentially influencing lipofuscin formation and their relevance for polar species are discussed. Factors explaining the pronounced differences in lipofuscin content between species for the moment remain unknown. The possibility for application of morphological lipofuscin as an index of age is encouraging for those investigated species with a sufficient accumulation rate of the pigment, and further studies will therefore be conducted