Paul Arthur Berkman

Antarctic Glacial History Since the Last Glacial Maximum: An Overview of the Record on Land

This overview examines available circum-Antarctic glacial history archives on land, related to developments after the Last Glacial Maximum (LGM). It considers the glacial-stratigraphic and morphologic records and also biostratigraphical information from moss banks, lake sediments and penguin rookeries, with some reference to relevant glacial marine records. It is concluded that Holocene environmental development in Antarctica differed from that in the Northern Hemisphere. The initial deglaciation of the shelf areas surrounding Antarctica took place before 10 000 14 C yrs before present( BP ), and was controlled by rising global sea level. This was followed by the deglaciation of some presently ice-free inner shelf and land areas between 10 000 and 8000 yr BP . Continued deglaciation occurred gradually between 8000 yr BP and 5000 yr BP . Mid-Holocene glacial readvances are recorded from various sites around Antarctica. There are strong indications of a circum-Antarctic climate warmer than today 4700–2000 yr BP . The best dated records from the Antarctic Peninsula and coastal Victoria Land suggest climatic optimums there from 4000–3000 yr BP and 3600–2600 yr BP , respectively. Thereafter Neoglacial readvances are recorded. Relatively limited glacial expansions in Antarctica during the past few hundred years correlate with the Little Ice Age in the Northern Hemisphere.

Pre-bomb radiocarbon and the reservoir correction for calcareous marine species in the Southern Ocean

Four Antarctic marine mollusc shells, which were collected alive between 1917 and 1940, were analyzed by accelerator mass spectrometry to provide the first pre-bomb radiocarbon measurements of biogenic carbonates from the Southern Ocean. After correcting for the impact of fossil fuel combustion (Suess Effect), radiocarbon activities of the pre-bomb shells averaged −149.8±10.4‰. In contrast, the Δ 14C values for post-bomb molluscs, echinoderms, brachiopods and foraminifera averaged −96.1±25.2‰. These biogenic carbonate Δ 14C values are nearly identical to pre-bomb estimates (-148‰ to −152‰) and post-bomb measurements (−98.4±22.0‰) of the surface waters in the Southern Ocean. Average radiocarbon ages of the biogenic carbonates before and after 1950 (1303±84 years and 811±205 years, respectively), along with those from seals and penguins, indicate that the Antarctic marine radiocarbon reservoir has decreased in age by nearly 500 years during the second half of the 20th century. Marine species and seawater measurements firmly place the radiocarbon reservoir correction at 1300±100 years for calcareous marine fossils which are widespread, abundant and well-preserved organic materials for interpreting ice-sheet, climate and sea level impacts on the Antarctic marine ecosystem during the Holocene.

Circum-Antarctic Coastal Environmental Shifts During the Late Quaternary Reflected by Emerged Marine Deposits

This review assesses the circumpolar occurrence of emerged marine macrofossils and sediments from Antarctic coastal areas in relation to Late Quaternary climate changes. Radiocarbon ages of the macrofossils, which are interpreted in view of the complexities of the Antarctic marine radiocarbon reservoir and resolution of this dating technique, show a bimodal distribution. The data indicate that marine species inhabited coastal environments from at least 35 000 to 20 000 yr BP, during Marine Isotope Stage 3 when extensive iceberg calving created a ‘meltwater lid’ over the Southern Ocean. The general absence of these marine species from 20 000 to 8500 yr BP coincides with the subsequent advance of the Antarctic ice sheets during the Last Glacial Maximum. Synchronous re-appearance of the Antarctic marine fossils in emerged beaches around the continent, all of which have Holocene marine-limit elevations an order of magnitude lower than those in the Arctic, reflect minimal isostatic rebound as relative sea-level rise decelerated. Antarctic coastal marine habitat changes around the continent also coincided with increasing sea-ice extent and outlet glacial advances during the mid-Holocene. In view of the diverse environmental changes that occurred around the Earth during this period, it is suggested that Antarctic coastal areas were responding to a mid-Holocene climatic shift associated with the hydrological cycle. This synthesis of Late Quaternary emerged marine deposits demonstrates the application of evaluating circum-Antarctic phenomena from the glacial-terrestrial-marine transition zone.

Zebra mussels invade Lake Erie muds

Zebra mussels (Dreissena polymorpha) originated in western Russia but have now become widespread in Europe and North America. They are widely known for their conspicuous invasion of rocks and other hard substrates in North American and European watersheds. We have found beds of zebra mussels (Fig. 1) directly colonizing sand and mud sediments each year across hundreds of square kilometres of North Americas Lake Erie. This transformation of sedimentary habitats into mussel beds represents an unforeseen change in the invasive capacity of this species.

Governance and Environmental Change in the Arctic Ocean

Strategies are being sought that will promote international cooperation and reduce the risks of discord in the Arctic Ocean.

Unprotected larval development in the Antarctic scallop Adamussium colbecki (Mollusca: Bivalvia: Pectinidae)

Most Antarctic bivalves are small and protect their young by holding fertilized eggs or larvae in their mantle cavities for varying periods. Nourishment for these early growth stages is provided by yolk reserves rather than by planktotrophy. The anomalously large Antarctic scallop, Adamussium colbecki, has unprotected planktotrophic larvae that are spawned during the austral spring. Successful recruitment of these larvae, in populations which are most abundant in oligotrophic habitats, may be associated with episodic pulses of organic material. Reasons why planktotrophy persists in A. colbecki are suggested by acomparison with another large Antarctic bivalve, Laternula elliptica. The latter has protected lecithotrophic larvae that are released at the beginning of the austral winter. This comparison suggests that unprotected larval development persists in A. colbecki because of unusual anatomical and ecological adaptations among the adults of the Adamussium lineage that have been evolving in the Southern Ocean since the early Oligocene.

Antarctic scallop (Adamussium colbecki) spatial population variability along the Victoria Land Coast, Antarctica

Abstract Along the Victoria Land Coast, the population structure of the Antarctic scallop (Adamussium colbecki) was studied in McMurdo Sound (New Harbor), Terra Nova Bay, and Wood Bay, on a latitudinal span of 3 degrees. At a large spatial scale, most relevant differences between the scallop populations are linked to their depth distributions. The McMurdo and Wood Bay populations show a shallower bathymetric distribution with maximum abundance between 5 and 15 m depth. In contrast, inside Terra Nova Bay, at sites with similar near-shore bathymetric profiles, the maximum biomass is found between 40 and 70 m. This difference can be related to the different ice-cover persistency characterising these two areas, being less at Terra Nova Bay than in the other localities. Differences arise also in the reproductive period: at McMurdo, it seems to occur early in the austral spring, while at Terra Nova Bay, mature females are observed at the beginning of February. Also at a small scale, in sites only a few miles from each other, the population structures inside Terra Nova Bay and Wood Bay vary in terms of abundance and size frequency distribution, suggesting various environmental and biological constraints. Among environmental factors, bottom features (slope, sediment grain size, organic content) and water-column food supply during the summer months may be considered. In addition, as Adamussium is preyed upon by starfishes and fishes, its abundance and population structure may be affected by predators and their abundance.

Winter sediment resuspension in McMurdo Sound, Antarctica, and its ecological implications

SummarySediment resuspension is a common phenomenon whose importance may be magnified in nearshore environments surrounding Antarctica, especially during the austral winter. Analyses suggest that sediments in the vicinity of McMurdo Station contain viable algal material throughout this period of darkness. The resuspension of these sediments, shown by sediment trap collections and underwater observations, would introduce organics into the water column and may provide an alternative food source for planktonic herbivores inhabiting near-shore environments during the Antarctic winter.

Habitat shift in invading species: Zebra and quagga mussel population characteristics on shallow soft substrates

Unexpected habitat innovations among invading species are illustrated by the expansion of dreissenid mussels across sedimentary environments in shallow water unlike the hard substrates where they are conventionally known. In this note, records of population characteristics of invading zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels from 1994 through 1998 are reported from shallow (less than 20 m) sedimentary habitats in western Lake Erie. Haphazard SCUBA collections of these invading species indicated that combined densities of zebra and quagga mussels ranged from 0 to 32,500 individuals per square meter between 1994 and 1998, with D. polymorpha comprising 75–100% of the assemblages. These mixed mussel populations, which were attached by byssal threads to each other and underlying sand-grain sediments, had size–frequency distributions that were typical of colonizing populations on hard substrates. Moreover, the presence of two mussel cohorts within the 1994 samples indicated that these species began expanding onto soft substrates not later than 1992, within 4 years of their initial invasion in western Lake Erie. Such historical data provide baselines for interpreting adaptive innovations, ecological interactions and habitat shifts among the two invading dreissenid mussel species in North America.

Ba, Ra, Th, and U in marine mollusc shells and the potential of 226Ra/Ba dating of Holocene marine carbonate shells

The geochemistry of Ba, Ra, Th, and U and the potential of using 226 Ra/Ba ratios as an alternative dating method are explored in modern and Holocene marine mollusc shells. Five modern shells of the Antarctic scallop Adamussium colbecki collected from the present day beach and six radiocarbon dated specimens from Holocene beach terraces of the Ross Sea region (Antarctic) between 700 and 6100 calibrated yr BP old have been analysed by mass spectrometry. In clean shells 226 Ra concentrations and 226 Ra/Ba ratios show a clear decrease with increasing age, suggesting the possibility of 226 Ra dating. Limiting factors for such dating are Ba and 226 Ra present in surface contaminants, and ingrowth of 226 Ra from U present within the shell. Surface contamination is difficult to clean off entirely, but moderate levels of residual contamination can be corrected using 232 Th. Sub-samples from the same shell with different proportions of contamination form a mixing line in a 226 Ra/Ba- 232 Th/Ba graph, and the 226 Ra/Ba of the pure shell can be derived from the intercept on the 226 Ra/Ba axis. Contaminant corrected 226 Ra/Ba ratios of late-Holocene 14 C-dated samples fall close to that expected from simple 226 Ra excess decay from seawater 226 Ra/Ba values. 226 Ra ingrowth from U incorporated into the shell during the lifetime of the mollusc can be corrected for. However, the unknown timing of post mortem U uptake into the shell makes a correction for 226 Ra ingrowth from secondary U difficult to achieve. In the A. colbecki shells, 226 Ra ingrowth from such secondary U becomes significant only when ages exceed 2500 yr. In younger shells, 226 Ra/Ba ratios corrected for surface contamination provide chronological information. If evidence for a constant oceanic relationship between 226 Ra and Ba in the ocean can be confirmed for that time scale, the 226 Ra/Ba chronometer may enable the reconstruction of variability in sea surface 14 C reservoir ages from mollusc shells and allow its use as a paleoceanographic