Spatial and temporal dynamics of coccolithophore communities during low production phases in the Norwegian-Greenland Sea

The present investigation was initiated to report on species compositions and dynamics in the Norwegian-Greenland Sea during low production phases in spring and early summer. Thus, the distribution patterns of living coccolithophores during June to July, 1990, February and May, 1991, and March to April, 1995 were investigated. In general, the seasonal development of the phytoplankton started after the yearly dark period and coccolithophores increased in abundance when the water column was more stratified and both temperatures and insolation increased. Cell densities reached a maximum of 207x10~c occospheres/l in the southeastern part of the studied area. However, these high cell densities probably resulted from ,,old" populations, drifted to the Norwegian-Greenland Sea from the North Atlantic. Some of the collected samples did not contain any coccolithophores. In total, 15 coccolithophore species were identified. The diversity was generally higher in the eastern part of the Norwegian-Greenland Sea and to the west the coccolithophore communities often were monospecific. Emiliania huxleyi is the dominant species, but Calciopappus caudatus and Algirosphaera robusta also considerably contribute to the communities. High cell densities of C. caudatus were interpreted as the result of a bloom or more probably close to bloom conditions during the general low productive period. In addition, many of the E. huxleyi coccolith from the surface waters of the southeastern Norwegian-Greenland Sea were heavily corroded. These specimens may have drifted within the Atlantic water for a longer time

Evidence for a steeper Eemian than Holocene sea surface temperature gradient between Arctic and sub-Arctic regions

Sediment proxy data from the Norwegian, Greenland, and Iceland seas (Nordic seas) are presented to evaluate surface water temperature (SST) differences between Holocene and Eemian times and to deduce from these data the particular mode of surface water circulation. Records from planktic foraminiferal assemblages, CaCO3 content, oxygen isotopes of foraminifera, and iceberg-rafted debris form the main basis of interpretation. All results indicate for the Eemian comparatively cooler northern Nordic seas than for the Holocene due to a reduction in the northwardly flow of Atlantic surface water towards Fram Strait and the Arctic Ocean. Therefore, the cold polar water flow from the Arctic Ocean was less influencial in the southwestern Nordic seas during this time. As can be further deduced from the Eemian data, slightly higher Eemian SSTs are interpreted for the western Iceland Sea compared to the Norwegian Sea (ca. south of 70°N). This Eemian situation is in contrast to the Holocene when the main mass of warmest Atlantic surface water flows along the Norwegian continental margin northwards and into the Arctic Ocean. Thus, a moderate northwardly decrease in SST is observed in the eastern Nordic seas for this time, causing a meridional transfer in ocean heat. Due to this distribution in SSTs the Holocene is dominated by a meridional circulation pattern. The interpretation of the Eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in SSTs

Calcareous phytoplankton response to the half century of interannual climatic variability in Santa Barbara Basin (California)

A high-resolution study of calcareous phytoplankton in a box core from the Santa Barbara Basin (SBB) reveals floral assemblage fluctuations which can be related to climatic and paleoceanographic changes during the last half century (1940-1996). In particular, Gephyrocapsa oceanica production increased during El Niño periods, in response to high temperatures, silica depletion, and increased iron availability. Conversely, Helicosphaera carteri flux increases in conjunction with lower surface temperatures associated with La Niña episodes. Increasing abundances of Florisphaera profunda and Umbilicosphaera sibogae after 1970 reflect a warming trend and increased stratification within the basin associated with the warm phase of the Pacific Decadal Oscillation (PDO). Conversely, increased abundances of Coccolithus pelagicus and Calcidiscus leptoporus before 1970 mark the cold phase of PDO. These coccolithophore production rate data are consistent with instrumental records of surface and thermocline temperatures monitored since 1950. This is the first study to document the response of calcareous phytoplankton to surface water warming occurring in SBB since 197

Gas hydrates: Entrance to a methane age or climate threat?

Methane hydrates, ice-like compounds in which methane is held in crystalline cages formed by water molecules, are widespread in areas of permafrost such as the Arctic and in sediments on the continental margins. They are a potentially vast fossil fuel energy source but, at the same time, could be destabilized by changing pressure-temperature conditions due to climate change, potentially leading to strong positive carbon-climate feedbacks. To enhance our understanding of both the vulnerability of and the opportunity provided by methane hydrates, it is necessary (i) to conduct basic research that improves the highly uncertain estimates of hydrate occurrences and their response to changing environmental conditions, and (ii) to integrate the agendas of energy security and climate change which can provide an opportunity for methane hydrates -- in particular if combined with carbon capture and storage -- to be used as a 'bridge fuel' between carbon-intensive fossil energies and zero-emission energies. Taken one step further, exploitation of dissociating methane hydrates could even mitigate against escape of methane to the atmosphere. Despite these opportunities, so far, methane hydrates have been largely absent from energy and climate discussions, including global hydrocarbon assessments and the Fourth Assessment Report of the Intergovernmental Panel on Climate Change

Evidence for a Warm Last Glacial Maximum in the Nordic Seas or an example of shortcomings in UK37' and UK37 to estimate low sea surface temperature?

The occurrence of ice-free conditions in the Nordic seas during the Last Glacial Maximum has been demonstrated using microfossil and biomarker approaches. An accurate picture of the prevailing oceanographic conditions may be more difficult to ascertain. Thus, uncertainties for most proxies increase at the cold extreme of temperature calibrations and glacial sediments contain small amounts of microfossils and biomarkers. Here we discuss sea surface temperature estimates derived from alkenone indices for the Last Glacial Maximum in the Nordic seas that provide a surprising scenario, where surface temperatures were warmer than at present. We conclude that the UK37' and UK37 estimates may not be interpreted in terms of sea surface temperature as several factors may have conspired to bias the molecular signal. However, using an alternative index based on the abundance of the C37∶4 alkenone, we estimate a maximum temperature of 6°C

Reconstruction of sea surface temperature variations in the Arabian Sea over the last 23 kyr using organic proxies (TEX86 and U37K')

Two sediment cores from the western Arabian Sea, NIOP905 and 74KL, were analyzed to determine sea surface temperature (SST) variations over the last 23 kyr. Two organic molecular SST proxies were used, the well-established U37K' based on long-chain unsaturated ketones synthesized by haptophyte algae and the newly proposed TEX86 derived from the membrane lipids of Crenarchaeota. Comparison of NIOP905 and 74KL core top data with present-day SST (0-10 m) values indicates that both proxies yield temperatures similar to local annual mean SSTs. However, TEX86 and U37K' SST down-core records derived from the same cores differ in magnitude and phasing. The alkenone SST record of NIOP905 shows small changes in SST (∼0.5°C) over the last 23 kyr, while that of core 74KL shows a ∼2°C increase from the Last Glacial Maximum (LGM) (23-19 calendar (cal) kyr B.P.) through the Holocene (the last 11.5 cal kyr B.P.) synchronous with changes in the Northern Hemisphere. In contrast, the TEX86 records of both cores show a large increase in SST from 22°-23°C in the LGM to 28°-30°C during Termination I (19-11.5 cal kyr B.P.), decreasing to present-day annual means of ∼26°C. A cold phase between 14.5 and 12 cal kyr B.P. that may correspond to the Antarctic cold reversal is also observed. This implies a Southern Hemisphere control on tropical SST reconstructed by the TEX86, possibly related to SW monsoon. Our results suggest that the application of both TEX86 and U37K' give different but complementary information on SST developments in past marine environments

A sea of Lilliputians

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 284 (2009): 88-113, doi:10.1016/j.palaeo.2009.08.020.Smaller size is generally seen as a negative response of organisms to stressful environmental conditions, associated with low diversity and species dominance. The mean size of the coccolithophorids decreased through the Neogene, leading to the prediction that their extant representatives are characterized by poor diversification and low specialization. The study of the (exo)coccospheres of selected taxa in the order Syracosphaerales negates this prediction, revealing that on the contrary some extant lineages are highly diversified and remarkably specialized. Whereas the general role of coccoliths remains indeterminate, this analysis suggests that some highly derived coccoliths may be modified for the collection of food particles, including picoplankton, thus implying that mixotrophy may characterize these lineages. In the extant coccolithophorids, species richness of genera is inversely correlated with the size of cells, definitive evidence that small size is part of a morphologic strategy rather than a sign of evolutionary failure. Because of their extreme minuteness, the extant nannoplankton can be well compared to Lilliputians, but the trend toward size decrease in Neogene lineages is not attributable to the Lilliput effect described by Urbanek (1993)