Opposed east-west climate response of the Arctic Ocean during the present interglacial.

The role of the Arctic Ocean in the global climate system during the last climatic cycles remains conjectural, but radiocarbon-based chronologies and proxy data provide reliable information about the present interglacial. In the western Arctic, paleoceanographic data demonstrate a linkage between increasing Pacific water fluxes, resulting from the postglacial submergence of the Bering Strait, and the progressive warming, until climate conditions stabilized when sea level reached its present-day limit during the late Holocene. Meanwhile, the southeastern Arctic Ocean evolved from optimal conditions toward a perennial sea ice cover with cooling.

Complex spatio-temporal structure of the Holocene Thermal Maximum.

Inconsistencies between Holocene climate reconstructions and numerical model simulations question the robustness of climate models and proxy temperature records. Climate reconstructions suggest an early-middle Holocene Thermal Maximum (HTM) followed by gradual cooling, whereas climate models indicate continuous warming. This discrepancy either implies seasonal biases in proxy-based climate reconstructions, or that the climate model sensitivity to forcings and feedbacks needs to be reevaluated.

The archaeology of climate change: The case for cultural diversity.

Anthropogenic climate change is currently driving environmental transformation on a scale and at a pace that exceeds historical records. This represents an undeniably serious challenge to existing social, political, and economic systems. Humans have successfully faced similar challenges in the past, however.

Natural variability of the Arctic Ocean sea ice during the present interglacial.

The impact of the ongoing anthropogenic warming on the Arctic Ocean sea ice is ascertained and closely monitored. However, its long-term fate remains an open question as its natural variability on centennial to millennial timescales is not well documented. Here, we use marine sedimentary records to reconstruct Arctic sea-ice fluctuations.

Rate of mass loss from the Greenland Ice Sheet will exceed Holocene values this century.

The Greenland Ice Sheet (GIS) is losing mass at a high rate. Given the short-term nature of the observational record, it is difficult to assess the historical importance of this mass-loss trend. Unlike records of greenhouse gas concentrations and global temperature, in which observations have been merged with palaeoclimate datasets, there are no comparably long records for rates of GIS mass change.

Publisher Correction: A global database of Holocene paleotemperature records.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Publisher Correction: A global database of Holocene paleotemperature records.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A global database of Holocene paleotemperature records.

A comprehensive database of paleoclimate records is needed to place recent warming into the longer-term context of natural climate variability. We present a global compilation of quality-controlled, published, temperature-sensitive proxy records extending back 12,000 years through the Holocene. Data were compiled from 679 sites where time series cover at least 4000 years, are resolved at sub-millennial scale (median spacing of 400 years or finer) and have at least one age control point every 3000 years, with cut-off values slackened in data-sparse regions.

Millennial-Scale Climate Variability and Dinoflagellate-Cyst-Based Seasonality Changes Over the Last ~150 kyrs at "Shackleton Site" U1385.

During the last glacial period, climate conditions in the North Atlantic region were determined by the alternation of relatively warm interstadials and relatively cool stadials, with superimposed rapid warming (Dansgaard-Oeschger) and cooling (Heinrich) events. So far little is known about the impact of these rapid climate shifts on the seasonal variations in sea surface temperature (SST) within the North Atlantic region. Here, we present a high-resolution seasonal SST record for the past 152 kyrs derived from Integrated Ocean Drilling Program "Shackleton" Site U1385, offshore Portugal.

Palynological data of cores MSM5/5-712-2 and PS2863/1-2 from northeastern Fram Strait spanning the last glacial maximum to present.

The palynogical data of two sites from northeastern Fram Strait (MSM5/5-712 and PS2863) encompassing the last 23,000 years are presented here. The data set first includes the palynomorph concentrations: dinocysts (cysts/g) and their fluxes (cysts/cm/yr) as well as pollen grains, spores, organic linings, , reworked palynomorphs and represented in #/g. It also includes the relative abundance (%) of dinocyst taxa at sites MSM5/5-712 and PS2863.

Environmental forcing on the flux of organic-walled dinoflagellate cysts in recent sediments from a subtropical lagoon in the Gulf of California.

To evaluate the relationship of changes in organic-walled dinoflagellate cyst (dinocyst) fluxes to sediments with environmental variables (air and sea surface temperatures, El Niño conditions, rainfall, and terrigenous index), cyst assemblages were analyzed in a Pb-dated sediment core (~100years) from the pristine San José Lagoon (San José Island, SW Gulf of California). The dinocyst abundance ranged from 3784 to 25,108cystsg and fluxes were of the order of 10-10cystscmyr. Lingulodinium machaerophorum, Polysphaeridium zoharyi and Spiniferites taxa accounted for 96% of the total dinocyst assemblages, and the abundances of these species increased towards the core surface.

First report of fossilized cysts produced by the benthic Bysmatrum subsalsum (Dinophyceae) from a shallow Mexican lagoon in the Gulf of Mexico.

Cysts belonging to the benthic dinoflagellate Bysmatrum subsalsum were recovered from palynologically treated sediments collected in the Alvarado Lagoon (southwestern Gulf of Mexico). The cysts are proximate, reflecting the features of the parent thecal stage, and their autofluorescence implies a dinosporin composition similar to the cyst walls of phototrophic species. This finding is important for our understanding of B.

Atlantic SSTs control regime shifts in forest fire activity of Northern Scandinavia.

Understanding the drivers of the boreal forest fire activity is challenging due to the complexity of the interactions driving fire regimes. We analyzed drivers of forest fire activity in Northern Scandinavia (above 60 N) by combining modern and proxy data over the Holocene. The results suggest that the cold climate in northern Scandinavia was generally characterized by dry conditions favourable to periods of regionally increased fire activity.

A new heterotrophic dinoflagellate from the North-eastern Pacific, Protoperidinium fukuyoi: cyst-theca relationship, phylogeny, distribution and ecology.

The cyst-theca relationship of Protoperidinium fukuyoi n. sp. (Dinoflagellata, Protoperidiniaceae) is established by incubating resting cysts from estuarine sediments off southern Vancouver Island, British Columbia, Canada, and San Pedro Harbor, California, USA.

Reconstruction of Pyrodinium blooms in the tropical East Pacific (Mexico): are they related to ENSO?

Some microplanktonic species, mostly dinoflagellates, causing Harmful Algal Blooms (HABs), produce toxins which may affect the environment and human health, thus causing important economic losses. The dinoflagellate Pyrodinium bahamense var. compressum is one of the main species causing harmful algal blooms along the tropical Pacific.

Reconstructed changes in Arctic sea ice over the past 1,450 years.

Arctic sea ice extent is now more than two million square kilometres less than it was in the late twentieth century, with important consequences for the climate, the ocean and traditional lifestyles in the Arctic. Although observations show a more or less continuous decline for the past four or five decades, there are few long-term records with which to assess natural sea ice variability. Until now, the question of whether or not current trends are potentially anomalous has therefore remained unanswerable.

Natural variability of Greenland climate, vegetation, and ice volume during the past million years.

The response of the Greenland ice sheet to global warming is a source of concern notably because of its potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice sheet by using pollen records from marine sediment off southwest Greenland that indicate important changes of the vegetation in Greenland over the past million years. The vegetation that developed over southern Greenland during the last interglacial period is consistent with model experiments, suggesting a reduced volume of the Greenland ice sheet.

Comment on "Mixed-layer deepening during Heinrich events: a multi-planktonic foraminiferal delta18O approach".

Rashid and Boyle (Reports, 19 October 2007, p. 439) analyzed oxygen isotopes in planktonic foraminera from marine sediments and concluded that Heinrich events (massive iceberg discharges into the North Atlantic Ocean) caused upper water masses to deepen. We question the robustness of this interpretation and argue that a strongly stratified mixed layer characterized by dense sea-ice cover and production of oxygen-18-depleted brines likely prevailed during such events.