Analysis of organic matter from DSDP Leg 81 Holes

Organic geochemical and visual kerogen analyses were carried out on approximately 50 samples from Leg 81 (Rockall Plateau, North Atlantic). The sediments are from four sites (Sites 552-555), Pleistocene to Paleocene in age, and represent significantly different depositional environments and sources of organic matter. The Pleistocene glacial-interglacial cycles show differences in sedimentary organic matter based on Rock-Eval pyrolysis, organic phosphorus, and pyrolysis/mass-spectrometry analyses. Glacial samples contain more organic carbon, with a larger proportion of reworked organic matter. This probably reflects increased erosion of continental and shelf areas as a result of low sea level stands. Inter glacial samples contain a larger proportion of marine organic matter as determined by organic phosphorus and pyrolysis analyses. This immature, highly oxidized marine organic matter may be associated with the skeletal organic matrix of calcareous organisms. In addition, Rock-Eval data indicate no significant inorganic-carbonate contribution to the S3 pyrolysis peak. The Pliocene-Miocene sediments consist of pelagic, biogenic carbonates. The organic matter is similar to that of the Pleistocene interglacial periods; a mixture of oxidized marine organic matter and reworked, terrestrial detritus. The Paleocene-Oligocene organic matter reflects variations in source and depositional factors associated with the isolation of Rockall from Greenland. Paleocene sediments contain primarily terrestrial organic matter with evidence of in situ thermal stress resulting from interbedded lava flows. Late Paleocene and early Eocene organic matter suggests a highly oxidized marine environment, with major periods of deposition of terrestrially derived organic matter. These fluctuations in organic-matter type are probably the result of episodic shallowing and deepening of Rockall Basins. The final stage of Eocene/Oligocene sedimentation records the accelerating subsidence of Rockall and its isolation from terrestrial sources (Rockall and Greenland). This is shown by the increasingly marine character of the organic matter. The petroleum potential of sediments containing more than 0.5% organic carbon is poor because of their thermal immaturity and their highly oxidized and terrestrial organic-matter composition.

(Table 1) Reproductive performance of brown skua pairs with and without feeding territories at Potter Peninsula/King George Island from 1998/1999 to 2000/2001

In the maritime Antarctic, brown skuas (Catharacta antarctica lonnbergi) show two foraging strategies: some pairs occupy feeding territories in penguin colonies, while others can only feed in unoccupied areas of a penguin colony without defending a feeding territory. One-third of the studied breeding skua population in the South Shetlands occupied territories of varying size (48 to >3,000 penguin nests) and monopolised 93% of all penguin nests in sub-colonies. Skuas without feeding territories foraged in only 7% of penguin sub-colonies and in part of the main colony. Females owning feeding territories were larger in body size than females without feeding territories; no differences in size were found in males. Territory holders permanently controlled their resources but defence power diminished towards the end of the reproductive season. Territory ownership guaranteed sufficient food supply and led to a 5.5 days earlier egg-laying and chick-hatching. Short distances between nest and foraging site allowed territorial pairs a higher nest-attendance rate such that their chicks survived better (71%) than chicks from skua pairs without feeding territories (45%). Due to lower hatching success in territorial pairs, no difference in breeding success of pairs with and without feeding territories was found in 3 years. We conclude that skuas owning feeding territories in penguin colonies benefit from the predictable and stable food resource by an earlier termination of the annual breeding cycle and higher offspring survivorship.

Age models of upper Pliocene samples of the North Atlantic

Abundance variations of six Pliocene species of discoasters have been analyzed over the time interval from 1.89 to 2.95 Ma at five contrasting sites in the North Atlantic: Deep Sea Drilling Project Sites 552 (56°N) and 607 (41°N) and Ocean Drilling Program 658 (20°N), 659 (18°N), and 662 (1°S). A sampling interval equivalent to approximately 3 k.y. was used. Total Discoaster abundance showed a reduction with increasing latitude and from the effects of upwelling. This phenomenon is most obvious in Discoaster brouweri, the only species that survived over the entire time interval studied. Prior to 2.38 Ma, Discoaster pentaradiatus and Discoaster surculus are important components of the Discoaster assemblage: Discoaster pentaradiatus increases slightly with latitude up to 41°N, and its abundance relative to D. brouweri increases up to 56°N; D. surculus increases in abundance with latitude and with upwelling conditions relative to both D. brouweri and D. pentaradiatus and is dominant to the latter species at upwelling Site 658 and at the highest latitude sites. Discoaster asymmetricus and Discoaster tamalis appear to increase in abundance with latitude relative to D. brouweri. Many of the abundance changes observed appear to be connected with the initiation of glaciation in the North Atlantic at 2.4 Ma. The long-term trend of decreasing Discoaster abundance probably reflects the fall of sea-surface temperatures. This trend of cooling is overprinted by short-term variations that are probably associated with orbital forcing. Evidence for the astronomical elements of eccentricity and obliquity periodicities were found at all sites; however, only at Sites 607, 659, and 662 were precessional periodicities detected. Furthermore, only at Site 659 was precession found to be dominant to obliquity. Abundance peaks of individual species were found to cross-correlate between sites. The distinct abundance fluctuations observed especially in the tropics suggest that temperature is not the only factor responsible for this variation. This study reveals for the first time the importance of productivity pressure on the suppression of Discoaster abundance.