Plant species, biomass and environmental characteristics of relevés along the North America Arctic bioclimate gradient

Question: How do interactions between the physical environment and biotic properties of vegetation influence the formation of small patterned-ground features along the Arctic bioclimate gradient? Location: At 68° to 78°N: six locations along the Dalton Highway in arctic Alaska and three in Canada (Banks Island, Prince Patrick Island and Ellef Ringnes Island). Methods: We analysed floristic and structural vegetation, biomass and abiotic data (soil chemical and physical parameters, the n-factor [a soil thermal index] and spectral information [NDVI, LAI]) on 147 microhabitat releves of zonalpatterned-ground features. Using mapping, table analysis (JUICE) and ordination techniques (NMDS). Results: Table analysis using JUICE and the phi-coefficient to identify diagnostic species revealed clear groups of diagnostic plant taxa in four of the five zonal vegetation complexes. Plant communities and zonal complexes were generally well separated in the NMDS ordination. The Alaska and Canada communities were spatially separated in the ordination because of different glacial histories and location in separate floristic provinces, but there was no single controlling environmental gradient. Vegetation structure, particularly that of bryophytes and total biomass, strongly affected thermal properties of the soils. Patterned-ground complexes with the largest thermal differential between the patterned-ground features and the surrounding vegetation exhibited the clearest patterned-ground morphologies.

Maestrichtian calcareous nannofossils of MAud Rise, Weddell Sea

Recovery of an essentially complete upper Maestrichtian/lower Paleocene interval on Maud Rise at 65 °S latitude in the Weddell Sea during Ocean Drilling Program Leg 113 marks the first time that this interval has been cored at these high latitudes. The entire interval was missing at all Falkland Plateau sites drilled during DSDP Legs 36 and 71. Maestrichtian nannofossil assemblages in sediments from Sites 689 and 690, therefore, provide the basis for a needed revision of Maestrichtian coccolith zonation schemes for high southern latitudes. Three zones and two new subzones are described: the uppermost Maestrichtian Nephrolithus frequens Zone, which is subdivided into the Cribrosphaerella daniae Subzone and the underlying N. corystus Subzone, and the Biscutum magnum and B. coronum Zones. A complete calcareous nannofossil biostratigraphy based on the proposed scheme is given including a description of individual species abundance, preservation, and stratigraphic distribution. At this site, the southernmost carbonate site yet drilled by DSDP/ODP, it is evident that the Falkland Plateau Nannofossil Biogeographic Province can be extended to the margins of Antarctica. In addition, the biogeographic ranges of many calcareous nannofossils can likewise be extended. Last, we hypothesize that Nephrolithus frequens evolved from N. corystus prior to its dispersal to the lower latitudes where it is an important zonal marker. Three new taxa, Neocrepidolithus watkinsii n. sp., Nephrolithus frequens miniporus emend, n. comb, and Psyktosphaera firthii n. gen., n. sp. are described.

(Table 2) Stable carbon and nitrogen isotope ratios and molar C/N ratio for euchaetid and aetideid copepods during POLARSTERN cruise ANT-XXIII/5

Stable isotope (SI) ratios of carbon (d13C) and nitrogen (d15N) were measured in omnivorous and carnivorous deep-sea copepods of the families Euchaetidae and Aetideidae across the Atlantic sector of the Southern Ocean to establish their trophic positions. Due to high and variable C/N ratios related to differences in lipid content, d13C was corrected using a lipid-normalisation model. d15N signals ranged from 3.0-6.9 per mil in mesopelagic species to 7.0-9.5 per mil in bathypelagic congeners. Among the carnivorous Paraeuchaeta species, the epi- to mesopelagic species Paraeuchaeta antarctica had lower d15N values than the mesopelagic P. rasa and bathypelagic P. barbata. The same trend was observed among omnivorous Aetideidae, but was not significant. In the most abundant species P. antarctica, individuals from the western Atlantic had higher d13C and d15N values than specimens at the eastern stations. These longitudinal changes in d13C and d15N values were attributed to regional differences in hydrography and sea surface temperature (SST), in particular related to a northward extension of the Antarctic Polar Front (APF) at the easternmost stations. The results indicate that even in a mesopelagic carnivorous species, the changes in surface stable isotope signatures are pronounced.

(Table 1) Distribution of upper Campanian-lower Maestrichtian calcareous nannofossils at DSDP Hole 71-511

Calcareous nannofossils from upper Campanian-lower Maestrichtian Deep Sea Drilling Project Leg 71 Cores 511-23 and 511-24 are described and correlated with assemblages of similar age from piston and drill cores on the Falkland Plateau, South Atlantic Ocean. The Leg 71 cores partially fill a drilling gap of at least 20 meters left within a thick (50 m) carbonate section first drilled by DSDP Leg 36 at Site 327. Cores 511-23 and 511-24 both fall within the upper portion of the Biscutum coronum Zone of Wind and demonstrate an overlap in the range of Monomarginatus quaternarius with the ranges of M. pectinatus, Misceomarginatus pleniporus, and Biscutum coronum across the Campanian/ Maestrichtian boundary. Resolution of the sequence of highest occurrence datums for the latter species must await the recovery of a more complete section. Comparison of the Site 511 assemblages with those from Mas Orcadas Core 07-75-44 to the north confirms earlier speculation that the Falkland Plateau served as an important boundary between major water masses during the Late Cretaceous.