Abstract: Abstract. Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousands of years before 1950) for Greenland ice cores. While several complementary orbital tuning tools have recently been developed using δ18Oatm, δO2⁄N2 and air content with different orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully understood. Here, we provide new series of δO2∕N2 and δ18Oatm data encompassing Marine Isotopic Stage (MIS) 5 (between 100 and 160 ka) and the oldest part (340–800 ka) of the East Antarctic EPICA Dome C (EDC) ice core. For the first time, the measurements over MIS 5 allow an inter-comparison of δO2∕N2 and δ18Oatm records from three East Antarctic ice core sites (EDC, Vostok and Dome F). This comparison highlights some site-specific δO2∕N2 variations. Such an observation, the evidence of a 100 ka periodicity in the δO2∕N2 signal and the difficulty to identify extrema and mid-slopes in δO2∕N2 increase the uncertainty associated with the use of δO2∕N2 as an orbital tuning tool, now calculated to be 3–4 ka. When combining records of δ18Oatm and δO2∕N2 from Vostok and EDC, we find a loss of orbital signature for these two parameters during periods of minimum eccentricity (∼ 400 ka, ∼ 720–800 ka). Our data set reveals a time-varying offset between δO2∕N2 and δ18Oatm records over the last 800 ka that we interpret as variations in the lagged response of δ18Oatm to precession. The largest offsets are identified during Terminations II, MIS 8 and MIS 16, corresponding to periods of destabilization of the Northern polar ice sheets. We therefore suggest that the occurrence of Heinrich–like events influences the response of δ18Oatm to precession.

Abstract: In: Le Groenland - Climat, Ecologie, Société (Editeurs: Masson-Delmotte, V., Gauthier, E., Grémillet, D., Huctin, JM, Swingedouw, D.). Editions du CNRS

Abstract: Pelagic seabirds are exposed to an array of potential threats during the non-breeding period, and effective management of these threats on a large scale requires knowledge of which populations winter where. Thick-billed murres (Uria lomvia) are emblematic of this conservation challenge, since they breed widely in the circumpolar Arctic, with many declining populations in the Atlantic. Threats facing murres include hunting, oil spills, bycatch and oceanic change influencing prey availability. Previous knowledge of migration pathways was insufficient to estimate the composition of various wintering populations. We collated tracking data (light-based geolocation) of 320 murres from 18 colonies in Canada, Greenland, Iceland, Svalbard and mainland Norway. Data were combined with breeding population counts to estimate the size and composition of wintering populations. The main wintering areas were off Newfoundland and Labrador, off West Greenland, and around Iceland. Winter areas were associated with the interface between High and Low Arctic ocean regimes. There was strong correspondence between wintering area and breeding population status: stable populations breeding in Canada and Northwest Greenland wintered mainly off Canada, whereas declining populations from Svalbard and Iceland wintered mainly off West Greenland and around Iceland. Many populations used distinct post-breeding areas, presumably for moulting; some of these areas were previously unknown. In some populations, there was a clear tendency for females to migrate south earlier than males, which accompany flightless fledglings when they leave the colony. Our study provides a key example of the urgency of coordinated, transoceanic management of vulnerable migratory species such as seabirds.

Abstract: Microplastics have been reported everywhere around the globe. With very limited human activities, the Arctic is distant from major sources of microplastics. However, microplastic ingestions have been found in several Arctic marine predators, confirming their presence in this region. Nonetheless, existing information for the Arctic remains scarce, thus there is an urgent need to quantify the contamination of marine waters in this part of the world. In this context, we studied microplastic abundance and composition within the zooplankton community off East Greenland. For the same area, we concurrently evaluated microplastic contamination of little auks (Alle alle), an Arctic seabird feeding on zooplankton while diving between 0-50 m. The study took place off East Greenland in July 2005 and 2014, under strongly contrasted sea ice conditions. Among all samples, 97.2 % of the debris found were filaments. Despite the remoteness of our study area, microplastic abundances were comparable to those of other ocean basins, with 0.99 ± 0.62m-3 in the presence of sea-ice (2005), and 2.38 ± 1.11m-3 in the nearby absence of sea-ice (2014). These results suggest that sea ice can represent a sink for microplastic particles, which are subsequently released to the water column upon the melting. Crucially, all birds studied had eaten plastic filaments, and little auks collected significantly higher levels of microplastics compared to background levels with 9.99 and 8.99 pieces per chick meal in 2005 and 2014, respectively. Importantly, we also demonstrated that little auks more often take light colored microplastics, rather than darker ones, strongly suggesting an active contamination with birds mistaking microplastics for their natural prey. Overall, our study stresses the great vulnerability of Arctic marine species to microplastic pollution in a warming Arctic, where sea-ice melting is expected to release vast volumes of trapped debris.

Abstract: Energy management models provide theories and predictions for how animals manage their energy budgets within their energetic constraints, in terms of their resting metabolic rate (RMR) and daily energy expenditure (DEE). Thus, uncovering what associations exist between DEE and RMR is key to testing these models. Accordingly, there is considerable interest in the relationship between DEE and RMR at both inter-and intraspecific levels. Interpretation of the evidence for particular energy management models is enhanced by also considering the energy spent specifically on costly activities (activity energy expenditure [AEE] = DEE 2 RMR). However, to date there have been few intraspecific studies investigating such patterns. Our aim was to determine whether there is a generality of intraspecific relationships among RMR, DEE, and AEE using long-term data sets for bird and mammal species. For mammals, we use minimum heart rate (f(H)), mean fH, and activity fH as qualitative proxies for RMR, DEE, and AEE, respectively. For the birds, we take advantage of calibration equations to convert fH into rate of oxygen consumption in order to provide quantitative proxies for RMR, DEE, and AEE. For all 11 species, the DEE proxy was significantly positively correlated with the RMR proxy. There was also evidence of a significant positive correlation between AEE and RMR in all four mammal species but only in some of the bird species. Our results indicate there is no universal rule for birds and mammals governing the relationships among RMR, AEE, and DEE. Furthermore, they suggest that birds tend to have a different strategy for managing their energy budgets from those of mammals and that there are also differences in strategy between bird species. Future work in laboratory settings or highly controlled field settings can tease out the environmental and physiological processes contributing to variation in energy management strategies exhibited by different species.Keywords