Late Pleistocene-Holocene radiolarian paleotemperatures in the Norwegian Sea based on artificial neural networks

Artificial Neural Networks (ANN) were trained by using an extensive radiolarian census dataset from the Nordic (Greenland, Norwegian, and Iceland) Seas. The regressions between observed and predicted Summer Sea Temperature (SST) indicate that lower error margins and better correlation coefficients are obtained for 100 m (SST₁₀₀) compared to 10 m (SST₁₀) water depth, and by using a subset of species instead of all species. The trained ANNs were subsequently applied to radiolarian data from two Norwegian Sea cores, HM 79-4 and MD95-2011, for reconstructions of SSTs through the last 15,000 years. The reconstructed SST is quite high during the Bølling-Allerød, when it reaches values only found later during the warmest phase of the Holocene. The climatic transitions in and out of the Younger Dryas are very rapid and involve a change in SST₁₀₀ of 6.2 and 6.8 °C, taking place over 440 and 140 years, respectively. SST₁₀₀ remains at a maximum during the early Holocene, and this Radiolarian Holocene Optimum Temperature Interval (RHOTI) predates the commonly recognized middle Holocene Climatic Optimum (HCO). During the 8.2 ka event, SST₁₀₀ decreases by ca. 3 °C, and this episode marks the establishment of a cooling trend, roughly spanning the middle Holocene (until ca. 4.2 ka). Successively, since then and through the late Holocene, SST₁₀₀ follows instead a statistically significant warming trend. The general patterns of the reconstructed SSTs agree quite well with previously obtained results based on application of Imbrie and Kipp Transfer Functions (IKTF) to the same two cores for SST₀. A statistically significant cyclic component of our SST record (period of 278 years) has been recognized. This is close to the de Vries or Suess cycle, linked to solar variability, and documented in a variety of other high-resolution Holocene records.     

On the hydrographic and ice conditions in the northern North Atlantic during different phases of a glaciation cycle

A theoretical investigation of the hydrographic conditions in the northern North Atlantic (N of the Greenland—Scotland Ridge) for different forcing conditions is undertaken. First a simple dynamical model for the “mediterranean” circulation in the Greenland and Norwegian seas (the Subpolar Sea) is developed. The calculated contemporary rate of deepwater formation (about 2.5 × 10⁶ m³/s) seems to be quite realistic. It is concluded that the mediterranean circulation is possible as long as the cyclonal atmospheric circulation in the Subpolar Sea is strong enough to prevent the fresher water in the coastal currents along the eastern and western boundaries from spreading over the interior.Utilizing the Arctic Ocean model in Stigebrandt (1981) the hydrographic and ice conditions in the Subpolar Sea and the Arctic Ocean during different phases of a glaciation are, finally, investigated. As so many parameters are involved the derivations are, by necessity, rather uncertain. However, it seems possible that the hydrographic state in the Subpolar Sea changes between mediterranean and estuarine circulation several times during a glacial cycle.     

Evaluating the efficacy of planktonic foraminifer calcite δO data for sea surface temperature reconstruction for the Late Miocene

This study examines the efficacy of published δ¹⁸O data from the calcite of Late Miocene surface dwelling planktonic foraminifer shells, for sea surface temperature estimates for the pre-Quaternary. The data are from 33 Late Miocene (Messinian) marine sites from a modern latitudinal gradient of 64°N to 48°S. They give estimates of SSTs in the tropics/subtropics (to 30°N and S) that are mostly cooler than present. Possible causes of this temperature discrepancy are ecological factors (e.g. calcification of shells at levels below the ocean mixed layer), taphonomic effects (e.g. diagenesis or dissolution), inaccurate estimation of Late Miocene seawater oxygen isotope composition, or a real Late Miocene cool climate. The scale of apparent cooling in the tropics suggests that the SST signal of the foraminifer calcite has been reset, at least in part, by early diagenetic calcite with higher δ¹⁸O, formed in the foraminifer shells in cool sea bottom pore waters, probably coupled with the effects of calcite formed below the mixed layer during the life of the foraminifera. This hypothesis is supported by the markedly cooler SST estimates from low latitudes—in some cases more than 9 °C cooler than present—where the gradients of temperature and the δ¹⁸O composition of seawater between sea surface and sea bottom are most marked, and where ocean surface stratification is high. At higher latitudes, particularly N and S of 30°, the temperature signal is still cooler, though maximum temperature estimates overlap with modern SSTs N and S of 40°. Comparison of SST estimates for the Late Miocene from alkenone unsaturation analysis from the eastern tropical Atlantic at Ocean Drilling Program (ODP) Site 958—which suggest a warmer sea surface by 2-4 °C, with estimates from oxygen isotopes at Deep Sea Drilling Project (DSDP) Site 366 and ODP Site 959, indicating cooler than present SSTs, also suggest a significant impact on the δ¹⁸O signal. Nevertheless, much of the original SST variation is clearly preserved in the primary calcite formed in the mixed layer, and records secular and temporal oceanographic changes at the sea surface, such as movement of the Antarctic Polar Front in the Southern Ocean. Cooler SSTs in the tropics and sub-tropics are also consistent with the Late Miocene latitude reduction in the coral reef belt and with interrupted reef growth on the Queensland Plateau of eastern Australia, though it is not possible to quantify absolute SSTs with the existing oxygen isotope data. Reconstruction of an accurate global SST dataset for Neogene time-slices from the existing published DSDP/ODP isotope data, for use in general circulation models, may require a detailed re-assessment of taphonomy at many sites.     

Nanobiology of the Ocean

Concepts of nanobiotic forms and their relationships with oceanic organic matter and feeding, as well as of their role in oceanic communities, are proposed on the basis of long-term electron microscope and microbiological studies initiated in 1969 in the Barents Sea, the Atlantic and Pacific oceans, and the marginal seas of the Arctic Ocean.     

The barnacles (Cirripedia: Thoracica) collected by the Viking expedition in chemobiotic benthic communities of the Norwegian and Barents Seas

The barnacles (Cirripedia Thoracica) collected by the Viking expedition in chemobiotic benthic communities of Arctic Ocean-Nyegga area in Norwegian Sea and Håkon Mosby Mud Volcano area in the Barents Sea are investigated. The species (Weltnerium nymphocola in Håkon Mosby Mud Volcano area and Hamatoscalpellum hamatum in Nyegga area) that were found are common inhabitants of the Barents and Norwegian sea benthic communities. The absence of obligatory barnacle fauna that was revealed in investigated chemobiotic benthic communities of the Arctic Ocean shows they are similar to corresponding communities of the Atlantic Ocean, while the specific obligatory barnacle fauna is noted for chemobiotic benthic communities of the Pacific and Indian oceans.     

Population status of Greenland halibut <Emphasis Type="Italic">Reinhardtius hippoglossoides</Emphasis> (Walbaum, 1793) of the Laptev Sea

This is the first study to perform a comparative genetic analysis of Greenland halibut in the samples from the Atlantic (waters of west and east of Greenland), Arctic (Laptev Sea), and Pacific (the western part of the Bering Sea) ocean basins using seven microsatellite loci. The obtained data clearly demonstrate that the Greenland halibut population in the Laptev Sea belongs to the groups of the Atlantic Ocean basin. Apparently, the Greenland halibut of the Laptev Sea is represented by a dependent population, which is replenished due to the drift of immatures from the spawning grounds in the Barents Sea with the transformed Atlantic water flow along the continental slope. In addition, the Arctic population can be partially replenished due to the breeding of the halibut in local spawning grounds.     

Security aspects of Danish and Norwegian law of the sea policies

Abstract

Denmark and Norway are strategically located near two of the major Soviet fleets stationed at Kaliningrad and Murmansk. In order for the Baltic Fleet stationed at Kaliningrad to gain access to the high seas of the North Atlantic Ocean, it must pass through the Belts, the Kattegat, the Skaggerak, and the North Sea or the Straits of Dover. In order for the Northern Fleet stationed at Murmansk to gain access to the high seas of the North Atlantic Ocean, it must pass through the Svalbard Passage between the North Cape of Norway and the Svalbard archipelago down through the Greenland‐Iceland‐United Kingdom (GIUK) gap. These strategic locations of Denmark and Norway give rise to several security issues that affect the law of the sea policies of both states.     

Diversity and trans-arctic invasion history of mitochondrial lineages in the North Atlantic Macoma balthica complex (Bivalvia: Tellinidae)

The history of repeated inter- or transoceanic invasions in bivalve mollusks of the circumpolar Macoma balthica complex was assessed from mtDNA COIII sequences. The data suggest that four independent trans-Arctic invasions, from the Pacific, gave rise to the current lineage diversity in the North Atlantic. Unlike in many other prominent North Atlantic littoral taxa, no evidence for (postinvasion) trans-Atlantic connections was found in the M. balthica complex. The earliest branch of the mtDNA tree is represented by the temperate-boreal North American populations (=Macoma petalum), separated from the M. balthica complex proper in the Early Pliocene at latest. The ensuing trans-Arctic invasions established the North European M. b. rubra, which now prevails on the North Sea and northeast Atlantic coasts, about two million years ago, and the currently northwest Atlantic M. balthica lineage in the Canadian Maritimes, in the Middle Pleistocene. The final reinvasion(s) introduced a lineage that now prevails in a number of North European marginal seas and is still hardly distinguishable from North Pacific mtDNA (M. b. balthica). We used coalescence simulation analyses to assess the age of the latest invasion from the Pacific to the northeast Atlantic. The results refute the hypothesis of recent, human-mediated reintroductions between northeast Pacific and the North European marginal seas in historical times. Yet they also poorly fit the alternative hypotheses of an early postglacial trans-Arctic invasion (< 11 thousand years ago), or an invasion during the previous Eemian interglacial (120 thousand years ago). Divergence time estimates rather fall in the Middle Weichselian before the Last Glacial Maximum, in conflict with the conventional thinking of trans-Arctic biogeographical connections; an early Holocene reinvasion may still be regarded as the most plausible scenario. Today, the most recently invaded Pacific mtDNA lineage is found admixed with the earlier established European Atlantic "rubra" lineage in the Baltic Sea and in Barents Sea populations east of the Varanger peninsula, and it is practically exclusive in the White and Pechora seas. Yet mtDNA does not always constitute an unequivocal taxonomic marker at individual level; the marginal populations represent hybrid swarms of the Atlantic and Pacific lineages in their nuclear genes.     

Mitochondrial DNA polymorphism of atlantic cod of the Barents and White seas

High level of intraspecific polymorphism of the mtDNA cytochrome b gene in the Atlantic cod Gadus morhua L. from the northeastern part of the species range (Barents and White seas) is detected. The absence of genetic differentiation between the samples from different areas of the Norwegian and Barents seas is shown, and the fact that these samples belong to the same population of Northeast Arctic cod is confirmed. Significant differences in the frequences of mitochondrial DNA haplotypes between the cod from the Barents and White seas, as well as from the northwestern part of the range, are found. The cod Gadus morhua kildinensis Derjugin, 1920 from Mogilnoye Lake and Gadus morhua marisalbi Derjugin, 1920 from the White Sea were revealed to have common haplotypes with the cod from the Barents Sea, confirming the recent origin of these forms from the Atlantic cod G. morhua.     

TEMPERATURE THRESHOLD AS A BIOGEOGRAPHIC BARRIER IN NORTHERN INDIAN OCEAN MACROALGAE1

The most eastern point of the Arabian Peninsula, Ras Al Hadd, marks the boundary between the Arabian Sea and the Gulf of Oman. This geographic landmark coincides with an abrupt floristic turnover, probably one of the sharpest biotic transitions known in marine biogeography. The floras of different Arabian localities across this floristic break were compared using macrophyte distribution data throughout the Indian Ocean and seasonal sea‐surface temperature (SST) data. The localities from the Arabian Gulf and Gulf of Oman differ significantly from those of the Arabian Sea based on their species richness, species composition, average distribution range per species, general temperature affinity of the composing species, and seasonal temperature data of the coastal waters. Pooling the temperature data into two groups (SST_3avg, average SST of the three warmest seasons; SST_min, minimum of the seasonal SSTs) revealed a temperature limit at 28°C using both the temperature affinity data of the floras and the seasonal temperatures recorded for the specific Arabian localities, which significantly separates the Arabian Sea from localities of both Gulfs. Finally, SST data of the Indian Ocean were analyzed using this upper temperature threshold of macrophytes at 28°C and the lower temperature limit of corals at 25°C, revealing general macrophyte diversity patterns.     

Psychrophilic versus psychrotolerant bacteria--occurrence and significance in polar and temperate marine habitats.

The numerical dominance and ecological role of psychrophilic bacteria in bottom sediments, sea ice, surface water and melt pools of the polar oceans were investigated using isolates, colony forming units (CFU) and metabolic activities. All sediment samples of the Southern Ocean studied showed a clear numerical dominance of cold-loving bacteria. In Arctic sediments underlying the influence of cold polar water bodies psychrophiles prevailed also but they were less dominant in sediments influenced by the warm Atlantic Water. A predominance of psychrophiles was further found in consolidated Antarctic sea ice as well as in multiyear Arctic sea ice and in melt pools on top of Arctic ice floes. A less uniform adaptation response was, however, met in polar surface waters. In the very northern part of the Fram Strait (Arctic Ocean) we found bacterial counts and activities at 1 degree C exceeding those at 22 degrees C. In surface water of the Weddell Sea (Southern Ocean) psychrophiles also dominated numerically in early autumn but the dominance declined obviously with the onset of winter-water and a decrease of chlorphyll a. Otherwise in surface water of the Southern Ocean CFUs were higher at 22 degrees C than at 1 degree C while activities were vice versa indicating at least a functional dominance of psychrophiles. Even in the temperate sediments of the German Bight true psychrophiles were present and a clear shift towards cold adapted communities in winter observed. Among the polar bacteria a more pronounced cold adaptation of Antarctic in comparison with Arctic isolates was obtained. The results and literature data indicate that stenothermic cold adapted bacteria play a significant role in the global marine environment. On the basis of the temperature response of our isolates from different habitats it is suggested to expand the definition of Morita in order to meet the cold adaptation strategies of the bacteria in the various cold habitats.     

The potential of organic-walled dinoflagellate cysts for the reconstruction of past sea-surface conditions in the Southern Ocean

In this study we investigate the potential of organic-walled dinoflagellate cysts (dinocysts) as tools for quantifying past sea-surface temperatures (SST) in the Southern Ocean. For this purpose, a dinocyst reference dataset has been formed, based on 138 surface sediment samples from different circum-Antarctic environments. The dinocyst assemblages of these samples are composed of phototrophic (gonyaulacoid) and heterotrophic (protoperidinioid) species that provide a broad spectrum of palaeoenvironmental information. The relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of Canonical Correspondence Analysis (CCA). Among the variables tested, summer SST appeared to correspond to the maximum variance represented in the dataset.To establish quantitative summer SST reconstructions, a Modern Analogue Technique (MAT) has been performed on data from three Late Quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the Atlantic sector of the Southern Ocean. These dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial/interglacial-cycles. During glacial conditions the relative abundance of protoperidinioid cysts was highest, whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts. The MAT palaeotemperature estimates show trends in summer SST changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140 000 years based on other proxies. However, by comparing the dinocyst results to quantitative estimates of summer SSTs based on diatoms, radiolarians and foraminifer-derived stable isotope records it can be shown that in several core intervals the dinocyst-based summer SSTs appeared to be extremely high. In these intervals the dinocyst record seems to be highly influenced by selective degradation, leading to unusual temperature ranges and to unrealistic palaeotemperatures. We used the selective degradation index (kt-index) to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates. We show that after correction the dinocyst based SSTs correspond reasonably well with other palaeotemperature estimates for this region, supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies.     

Increased intrusion of warming Atlantic water leads to rapid expansion of temperate phytoplankton in the Arctic

The Arctic Ocean and its surrounding shelf seas are warming much faster than the global average, which potentially opens up new distribution areas for temperate‐origin marine phytoplankton. Using over three decades of continuous satellite observations, we show that increased inflow and temperature of Atlantic waters in the Barents Sea resulted in a striking poleward shift in the distribution of blooms of Emiliania huxleyi, a marine calcifying phytoplankton species. This species' blooms are typically associated with temperate waters and have expanded north to 76°N, five degrees further north of its first bloom occurrence in 1989. E. huxleyi's blooms keep pace with the changing climate of the Barents Sea, namely ocean warming and shifts in the position of the Polar Front, resulting in an exceptionally rapid range shift compared to what is generally detected in the marine realm. We propose that as the Eurasian Basin of the Arctic Ocean further atlantifies and ocean temperatures continue to rise, E. huxleyi and other temperate‐origin phytoplankton could well become resident bloom formers in the Arctic Ocean.     

The potential of organic-walled dinoflagellate cysts for the reconstruction of past sea-surface conditions in the Southern Ocean

In this study we investigate the potential of organic-walled dinoflagellate cysts (dinocysts) as tools for quantifying past sea-surface temperatures (SST) in the Southern Ocean. For this purpose, a dinocyst reference dataset has been formed, based on 138 surface sediment samples from different circum-Antarctic environments. The dinocyst assemblages of these samples are composed of phototrophic (gonyaulacoid) and heterotrophic (protoperidinioid) species that provide a broad spectrum of palaeoenvironmental information. The relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of Canonical Correspondence Analysis (CCA). Among the variables tested, summer SST appeared to correspond to the maximum variance represented in the dataset.To establish quantitative summer SST reconstructions, a Modern Analogue Technique (MAT) has been performed on data from three Late Quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the Atlantic sector of the Southern Ocean. These dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial/interglacial-cycles. During glacial conditions the relative abundance of protoperidinioid cysts was highest, whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts. The MAT palaeotemperature estimates show trends in summer SST changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140 000 years based on other proxies. However, by comparing the dinocyst results to quantitative estimates of summer SSTs based on diatoms, radiolarians and foraminifer-derived stable isotope records it can be shown that in several core intervals the dinocyst-based summer SSTs appeared to be extremely high. In these intervals the dinocyst record seems to be highly influenced by selective degradation, leading to unusual temperature ranges and to unrealistic palaeotemperatures. We used the selective degradation index (kt-index) to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates. We show that after correction the dinocyst based SSTs correspond reasonably well with other palaeotemperature estimates for this region, supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies.     

Biology of the Greenland shark Somniosus microcephalus

Greenland shark Somniosus microcephalus is a potentially important yet poorly studied cold-water species inhabiting the North Atlantic and Arctic Oceans. Broad-scale changes in the Arctic ecosystem as a consequence of climate change have led to increased attention on trophic dynamics and the role of potential apex predators such as S. microcephalus in the structure of Arctic marine food webs. Although Nordic and Inuit populations have caught S. microcephalus for centuries, the species is of limited commercial interest among modern industrial fisheries. Here, the limited historical information available on S. microcephalus occurrence and ecology is reviewed and new catch, biological and life-history information from the Arctic and North Atlantic Ocean region is provided. Given the considerable by-catch rates in high North Atlantic Ocean latitudes it is suggested that S. microcephalus is an abundant predator that plays an important, yet unrecognized, role in Arctic marine ecosystems. Slow growth and large pup sizes, however, may make S. microcephalus vulnerable to increased fishing pressure in a warming Arctic environment.     

High resolution Holocene palynological record from the Scotian Shelf

Because of their location at the confluence of polar and subtropical airmasses and near a transition zone between the cold Labrador Current and the Gulf Stream, the Atlantic Provinces experience some of the most dynamic climate conditions in Canada. Major climate changes occurred during the Holocene, as shown by pollen records from lakes, but previous paleoceanographic studies, based on low-resolution proxy-data records do not show major changes during the past 8000 years. Therefore, the Holocene history of Canada's Atlantic region was examined using a high-resolution palynological record from the Scotian Shelf (La Have Basin). Sea surface conditions were reconstructed using proxy-data from dinoflagellate cysts and paleobioclimatic transfer functions. Ocean–atmosphere interactions are determined by onshore–offshore correlation of marine and pollen records from Nova Scotia.Results show a succession of major paleoceanographic events. Sea surface temperatures (SST) (February and August) up to 5°C higher than today's average and slightly higher salinity are reconstructed between 10.5 and 8.5 ka. The last pulse of meltwater from the residual ice sheet affected the shelf waters between 8.5 and 6.5 ka by lowering the SST (in February) and the salinity. Most previous studies failed to record this event. Since 6.5 ka, August temperature generally remained around today's value, while February temperature was generally 2°C above it, except for recurring colder and lower salinity intervals. These cold intervals have a recurrence of about 1000 years. A slight cooling of summer SST is recorded in the last 500 years.Comparison with climatic reconstructions from Nova Scotia pollen records shows a difference in timing between ocean and atmosphere. The onset of the climatic optimum (hypsithermal) in Nova Scotia lags by about 2000 years (until 8 ka) relative to the ocean but it lasted longer. The Neoglacial cooling in Atlantic Canada however, started earlier (2 ka) than the late Holocene ocean cooling.La Have Basin's Holocene paleoceanography presents some differences from most other studies from the region: (1) the hypsithermal started earlier; (2) the last pulse of meltwater is recorded; (3) the last 6500 years are punctuated by colder intervals.Increased productivity and blooms of toxic algae in the early Holocene are probably due to a combination of factors: increased nutrients and a greater stability of the water column because of meltwaters, higher SST and increased upwelling or storm activity.     

The role of the North Atlantic Drift in the millennial timescale glacial climate fluctuations

The Greenland ice core records show that the overall cold climate of the last glacial period was repeatedly interrupted by short, rapid warmings. The events, known as Dansgaard-Oeschger (D-O) events, are strongly imprinted in the North Atlantic marine records suggesting that they were linked to North Atlantic circulation changes. However, the causes of the D-O events are poorly understood and they represent one of the most intriguing puzzles of the last glacial period. In order to investigate a possible mechanism we have studied variations in the distribution of benthic and planktonic foraminifera, oxygen isotopes and ice rafted debris during the last glacial period in eight cores from the North Atlantic and the Nordic Seas taken at mid depth from 853 to 1760 m. The parameters indicate, in agreement with previous studies, that the circulation system during the interstadials resembled the present system. Atlantic surface water flowed north into the Nordic Seas, where most of it sank through convection and, as cold deep water, flowed back into the North Atlantic. During the stadials, a halocline was established in the Nordic Seas and in the northernmost part of the North Atlantic and the outflow from the Nordic Seas stopped. However, below the cold, light surface layer, the relatively warm water of the North Atlantic Drift continued to flow across the North Atlantic and into the Nordic Seas, here warming up the deep-water masses. We suggest that the warm water gradually made the water column unstable. The pivotal abrupt climate warmings were caused by sudden upwelling of the deep, warm water masses causing overturning of the entire water column and onset of convection.     

Seasonal occurrence of picocyanobacteria in the Greenland Sea and central Arctic Ocean

The seasonal occurrence of picocyanobacteria in the Greenland Sea and Arctic Ocean was investigated during four expeditions in May–June 1987 and 1988, August–October 1991, and November–December 1988 by epifluorescence microscopy. In early summer, the abundance of picocyanobacteria was related to water masses: they were nearly absent in polar water, whereas they occurred in high concentrations (up to 5470 cells ml^–1) in Atlantic Water. During autumn and beginning of winter, the abundances of picocyanobacteria remained around 10³ cells ml^–1. Their relative contribution to total picoplanktonic algal abundance increased from 0% during spring/summer to 70–80% in late autumn, as a result of a decrease in the abundance of eucaryotic picoalgae. Consequently, the impact of picocyanobacteria on Arctic epipelagic carbon and energy flow is of minor importance, and the strong contribution of picoplankton algae to biomass and primary productivity in Arctic seas has to be attributed to eucaryotic species.     

The role of sea ice for vascular plant dispersal in the Arctic

Sea ice has been suggested to be an important factor for dispersal of vascular plants in the Arctic. To assess its role for postglacial colonization in the North Atlantic region, we compiled data on the first Late Glacial to Holocene occurrence of vascular plant species in East Greenland, Iceland, the Faroe Islands and Svalbard. For each record, we reconstructed likely past dispersal events using data on species distributions and genetics. We compared these data to sea-ice reconstructions to evaluate the potential role of sea ice in these past colonization events and finally evaluated these results using a compilation of driftwood records as an independent source of evidence that sea ice can disperse biological material. Our results show that sea ice was, in general, more prevalent along the most likely dispersal routes at times of assumed first colonization than along other possible routes. Also, driftwood is frequently dispersed in regions that have sea ice today. Thus, sea ice may act as an important dispersal agent. Melting sea ice may hamper future dispersal of Arctic plants and thereby cause more genetic differentiation. It may also limit the northwards expansion of competing boreal species, and hence favour the persistence of Arctic species.