Catherine Jessen

Late-Holocene sea-surface conditions offshore Newfoundland based on dinoflagellate cysts

Dinoflagellate cysts and XRF core scanning data from two marine sediment cores from embayments north (Bonavista Bay) and south (Placentia Bay) of Newfoundland show significant changes in ocean and atmospheric conditions of the SW Labrador Sea region during the last 5700 years. Fresh and cold conditions, probably accompanied by seasonal sea ice, prevailed both north and south of Newfoundland from c. 5.7 to 4.0 cal. kyr BP. This may be linked to intensified Labrador Current export of cold meltwater and/or sea ice from the Arctic, presumably related to warmer conditions in the northernmost latitudes and the prevalence of strong (north)westerly winds. After c. 4.0 cal. kyr BP, sea-surface conditions warmed up and sea ice decreased northeast of Newfoundland, but conditions were still cold south of Newfoundland. This suggests a decrease in Arctic meltwater export and westerly wind strength. After 2.9—2.5 cal. kyr BP, only minor changes in sea-surface conditions affected the study sites. Sea-surface temperatures increased and sea ice decreased at both sites, which may be related to a more meridional atmospheric circulation pattern associated with the general Northern Hemisphere neoglacial cooling. In Placentia Bay the warmest part of the record corresponds to the Roman Warm Period, while the warmest part of the records in Bonavista Bay notably corresponds to the Dark Ages.

Rapid Holocene climate changes in the North Atlantic: evidence from lake sediments from the Faroe Islands

Holocene records from two lakes on the Faroe Islands were investigated to determine regional climatic variability: the fairly wind-exposed Lake Starvatn on Streymoy and the more sheltered Lake Lykkjuvotn on Sandoy. Sediment cores were analysed for content of biogenic silica, organic carbon and clastic material, and magnetic susceptibility. In addition, a new qualitative proxy for past lake ice cover and wind activity was developed using the flux of clastic grains that are larger than 255 mu m. Both long-term and short-term climatic developments were similar between the two lakes, suggesting a response to a regional climate signal. The long-term climate development is characterized by early Holocene rapid warming followed by Holocene climatic optimum conditions ending around 8300 cal. yr BP. A more open landscape as evidenced from increased sand grain influx in the period 8300-7200 cal. yr BP could reflect the aftermath of the 8200 cal. yr BP event, although the event itself is not recognized in either of the two lake records. From around 7200 cal. yr BP the mid-Holocene climate deterioration is observed and from 4200 cal. yr BP the climate deteriorated further with increased amplitude of centennial cooling episodes. (Less)

Variability and seasonality of North Atlantic climate during the early Holocene: evidence from Faroe Island lake sediments

Based on their position in relation to major ocean currents, palaeoclimatic archives in the Faroe Islands are expected to be sensitive recorders of variations in North Atlantic circulation. The multiproxy analysis (magnetic susceptibility, total carbon, nitrogen and sulphur, biogenic silica, grains >255 µm) of a lacustrine record with both winter and summer climate indicators illustrates the variability of Faroese climate during the early Holocene (c. 11 300—10 240 cal. yr BP) and allows comparison with other records in the region. Our high-resolution record suggests a period of predominantly winter cooling and increased storminess centred at c. 11 150 cal. yr BP followed by a period of stability between c. 11 000 and 10 680 cal. yr BP, which correlates with a time when the North Atlantic was particularly free of meltwater incursions. After c. 10 680 cal. yr BP, both winter and summer indicators show an increase in variability broadly synchronous with increased variability at other North Atlantic sites. Within this time period, a predominantly winter cooling centred at c. 10 600 cal. yr BP, a winter/summer cooling centred at c. 10 450 cal. yr BP and a winter/summer cooling centred at c. 10 300 cal. yr BP are recorded. These distinctive coolings correspond to periods of ice core δ18O inferred lowered atmospheric temperatures over Greenland and the reoccurrence of meltwater outbursts at c. 10 600, 10 500 and 10 350 cal. yr BP.

A late Holocene palaeoenvironmental record from Altona Bay, St. Croix, US Virgin Islands

Abstract Geografisk Tidsskrift, Danish Journal of Geography 108(2):59–70, 2008 A reconstruction of the palaeoenvironmental development of Altona Bay, St. Croix, northeastern Caribbean, has been made based on the sedimentological, geochemical and pollen analyses of a 1.83 m long vibracore. For chronological control, AMS 14C measurements were made at 5 levels downcore. The sedimentary sequence covers the last c. 4,700 years, containing both (mangrove) peat and fine-grained clastic sediment units. Comparison with regional Holocene sea level data demonstrates a gradual marine flooding of a mangrove environment around 3,500 cal BP was presumably related to a regional late Holocene sea-level rise, from a position, c. 2 m lower than present. After a c. 1,000 year period of marine sedimentation lasting until c. 2,500 cal BP, renewed formation of tropical wetland occurred at the site. This development may be attributed to the increased isolation of the shallow Altona Bay, most likely due to sea- ward formation of a well-developed spit system and possibly under the influence of enhanced storm-wave action in the period between c. 4,000 and 2,200 cal BP. Since the 1960s the repeated passage of severe hurricanes (e.g. Hugo, 1989) has had a significant impact on the sedimentation pattern of the bay and has caused a major hiatus and the recent deposition of sediments immediately overlying the c. 2,500 year old peat.