Element concentrations and Osmium, Platinum and Rhenium isotope ratios of ODP Site 153-920 abyssal peridotites

Abyssal peridotites are normally thought to be residues of melting of the mid-ocean ridge basalt (MORB) source and are presumably a record of processes affecting the upper mantle. Samples from a single section of abyssal peridotite from the Kane Transform area in the Atlantic Ocean were examined for 190Pt-186Os and 187Re-187Os systematics. They have uniform 186Os/188Os ratios with a mean of 0.1198353 +/- 7, identical to the mean of 0.1198340 +/-12 for Os-Ir alloys and chromitites believed to be representative of the upper mantle. While the Pt/Os ratios of the upper mantle may be affected locally by magmatic processes, these data show that the Pt/Os ratio for the bulk upper mantle has not deviated by more than about +/- 30% from a chondritic Pt/Os ratio over 4.5 billion years. These observations are consistent with the addition of a chondritic late veneer after core separation as the primary control on the highly siderophile element budget of the terrestrial upper mantle. The 187Os/188Os of the samples range from 0.12267 to 0.12760 and correlate well with Pt and Pt/Os, but not Re/Os. These relationships may be explained by variable amounts of partial melting with changing D(Re), reflecting in part garnet in the residue, with a model-dependent melting age between about 600 and 1700 Ma. A model where the correlation between Pt/Os and 187Os/188Os results from multiple ancient melting events, in mantle peridotites that were later juxtaposed by convection, is also consistent with these data. This melting event or events are evidently unrelated to recent melting under mid-ocean ridges, because recent melting would have disturbed the relationship between Pt/Os and 187Os/188Os. Instead, this section of abyssal peridotite may be a block of refractory mantle that remained isolated from the convecting portions of the upper mantle for 600 Ma to >1 Ga. Alternatively, Pt and Os may have been sequestered during more recent melting and possibly melt/rock reaction processes, thereby preserving an ancient melting history. If representative of other abyssal peridotites, then the rocks from this suite with subchondritic 187Os/188Os are not simple residues of recent MORB source melting at ridges, but instead have a more complex history. This suite of variably depleted samples projects to an undepleted present-day Pt/Os of about 2.2 and 187Os/188Os of about 0.128-0.129, consistent with estimates for the primitive upper mantle.

Contaminant concentrations in ivory gull (Pagophila eburnea) eggs from Svalbard and the Russian Arctic (2006-2007)

We found high levels of contaminants, in particular organochlorines, in eggs of the ivory gull Pagophila eburnea, a high Arctic seabird species threatened by climate change and contaminants. An 80% decline in the ivory gull breeding population in the Canadian Arctic the last two decades has been documented. Because of the dependence of the ivory gull on sea ice and its high trophic position, suggested environmental threats are climate change and contaminants. The present study investigated contaminant levels (organochlorines, brominated flame retardants, perfluorinated alkyl substances, and mercury) in ivory gull eggs from four colonies in the Norwegian Svalbard) and Russian Arctic (Franz Josef Land and Severnaya Zemlya). The contaminant levels presented here are among the highest reported in Arctic seabird species, and we identify this as an important stressor in a species already at risk due to environmental change.

Concentrations of persistant organic pollutants in Great skua eggs (Stercorarius skua) from Shetland 1980 and 2008

Concentrations of POPs in Great skua eggs from Shetland are among the highest in North Atlantic seabirds, with up to 11,600 µg/kg (ww) DDE and up to 17,900 µg/kg ww SumPCB. Concentrations of legacy POPs were significantly lower in 2008 than 1980. Decreases were greatest for least persistent compounds. Median SumPBDEs increased from 99 µg/kg ww in 1980 to 173 µg/kg ww in 2008. There were changes in Great skua breeding season diet, with more adult Herring and Mackerel and less Sandeel. These changes increase exposure to POPs, since Herring and Mackerel accumulate more POPs than Sandeels. In both years, eggs with higher d15N had higher POP concentrations. In 1980, birds feeding more on demersal discard fish from trawl fisheries and less on Sandeels, had higher POP levels in eggs. In 2008, individuals feeding more on Herring and Mackerel, and less on discards, had higher POP levels in eggs.

(Table 1) Circulating levels of TT3 and TT4, and age, length, girth, and estimated body mass in polar bears (Ursus maritimus) from East Greenland 1999-2001

We investigated the multivariate relationships between adipose tissue residue levels of 48 individual organohalogen contaminants (OHCs) and circulating thyroid hormone (TH) levels in polar bears (Ursus maritimus) from East Greenland (1999-2001, n = 62), using projection to latent structure (PLS) regression for four groupings of polar bears; subadults (SubA), adult females with cubs (AdF_N), adult females without cubs (AdF_S) and adult males (AdM). In the resulting significant PLS models for SubA, AdF_N and AdF_S, some OHCs were especially important in explaining variations in circulating TH levels: polybrominated diphenylether (PBDE)-99, PBDE-100, PBDE-153, polychlorinated biphenyl (PCB)-52, PCB-118, cis-nonachlor, trans-nonachlor, trichlorobenzene (TCB) and pentachlorobenzene (QCB), and both negative and positive relationships with THs were found. In addition, the models revealed that DDTs had a positive influence on total 3,5,3'-triiodothyronine (TT3) in AdF_S, and that a group of 17 higher chlorinated ortho-PCBs had a positive influence on total 3,5,3',5'-tetraiodothyronine (thyroxine, TT4) in AdF_N. TH levels in AdM seemed less influenced by OHCs because of non-significant PLS models. TH levels were also influenced by biological factors such as age, sex, body size, lipid content of adipose tissue and sampling date. When controlling for biological variables, the major relationships from the PLS models for SubA, AdF_N and AdF_S were found significant in partial correlations. The most important OHCs that influenced TH levels in the significant PLS models may potentially act through similar mechanisms on the hypothalamic-pituitary-thyroid (HPT) axis, suggesting that both combined effects by dose and response addition and perhaps synergistic potentiation may be a possibility in these polar bears. Statistical associations are not evidence per se of biological cause-effect relationships. Still, the results of the present study indicate that OHCs may affect circulating TH levels in East Greenland polar bears, adding to the "weight of evidence" suggesting that OHCs might interfere with thyroid homeostasis in polar bears.