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Integrated sediment multiproxy studies and modeling were used to reconstruct past changes in the Baltic Sea ecosystem. Results of natural changes over the past 6000 years in the Baltic Sea ecosystem suggest that forecasted climate warming might enhance environmental problems of the Baltic Sea. Integrated modeling and sediment proxy studies reveal increased sea surface temperatures and expanded seafloor anoxia (in deep basins) during earlier natural warm climate phases, such as the Medieval Climate Anomaly. Under future IPCC scenarios of global warming, there is likely no improvement of bottom water conditions in the Baltic Sea. Thus, the measures already designed to produce a healthier Baltic Sea are insufficient in the long term. The interactions between climate change and anthropogenic impacts on the Baltic Sea should be considered in management, implementation of policy strategies in the Baltic Sea environmental issues, and adaptation to future climate change.

The Pikialasorsuaq (North Water polynya) is an area of local and global cultural and ecological significance. However, over the last decades, the region has been subject to rapid warming, and in some recent years, the seasonal ice arch that has historically defined the polynya's northern boundary has failed to form. Both factors are deemed to alter the polynya's ecosystem functioning. To understand how climate‐induced changes to the Pikialasorsuaq impact the basis of the marine food web, we explored diatom community‐level responses to changing conditions, from a sediment core spanning the last 3800 years. Four metrics were used: total diatom concentrations, taxonomic composition, mean size, and diversity. Generalized additive model statistics highlight significant changes at ca. 2400, 2050, 1550, 1200, and 130 cal years BP, all coeval with known transitions between colder and warmer intervals of the Late Holocene, and regime shifts in the Pikialasorsuaq. Notably, a weaker/contracted polynya during the Roman Warm Period and Medieval Climate Anomaly caused the diatom community to reorganize via shifts in species composition, with the presence of larger taxa but lower diversity, and significantly reduced export production. This study underlines the high sensitivity of primary producers to changes in the polynya dynamics and illustrates that the strong pulse of early spring cryopelagic diatoms that makes the Pikialasorsuaq exceptionally productive may be jeopardized by rapid warming and associated Nares Strait ice arch destabilization. Future alterations to the phenology of primary producers may disproportionately impact higher trophic levels and keystone species in this region, with implications for Indigenous Peoples and global diversity. [ABSTRACT FROM AUTHOR]

High Arctic ecosystems and Indigenous livelihoods are tightly linked and exposed to climate change, yet assessing their sensitivity requires a long-term perspective. Here, we assess the vulnerability of the North Water polynya, a unique seaice ecosystem that sustains the world's northernmost Inuit communities and several keystone Arctic species. We reconstruct mid-to-late Holocene changes in sea ice, marine primary production, and little auk colony dynamics through multi-proxy analysis of marine and lake sediment cores. Our results suggest a productive ecosystem by 4400–4200 cal yrs b2k coincident with the arrival of the first humans in Greenland. Climate forcing during the late Holocene, leading to periods of polynya instability and marine productivity decline, is strikingly coeval with the human abandonment of Greenland from c. 2200–1200 cal yrs b2k. Our long-term perspective highlights the future decline of the North Water ecosystem, due to climate warming and changing sea-ice conditions, as an important climate change risk. The North Water polynya is a unique but vulnerable ecosystem, home to Indigenous people and Arctic keystone species. New palaeoecological records from Greenland suggest human abandonment c. 2200–1200 cal yrs BP occurred during climate-forced polynya instability, foreshadowing future ecosystem declines. [ABSTRACT FROM AUTHOR]

Climate warming is rapidly reshaping the Arctic cryosphere and ocean conditions, with consequences for sea ice and pelagic productivity patterns affecting the entire marine food web. To predict how ongoing changes will impact Arctic marine ecosystems, concerted effort from various disciplines is required. Here, we contribute multi‐decadal reconstructions of changes in diatom production and sea‐ice conditions in relation to Holocene climate and ocean conditions off northwest Greenland. Our multiproxy study includes diatoms, sea‐ice biomarkers (IP25 and HBI III) and geochemical tracers (TOC [total organic carbon], TOC:TN [total nitrogen], δ13C, δ15N) from a sediment core record spanning the last c. 9,000 years. Our results suggest that the balance between the outflow of polar water from the Arctic, and input of Atlantic water from the Irminger Current into the West Greenland Current is a key factor in controlling sea‐ice conditions, and both diatom phenology and production in northeastern Baffin Bay. Our proxy record notably shows that changes in sea‐surface conditions initially forced by Neoglacial cooling were dynamically amplified by the shift in the dominant phase of the Arctic Oscillation (AO) mode that occurred at c. 3,000 yr BP, and caused drastic changes in community composition and a decline in diatom production at the study site. In the future, with projected dominant‐positive AO conditions favored by Arctic warming, increased water column stratification may counteract the positive effect of a longer open‐water growth season and negatively impact diatom production. [ABSTRACT FROM AUTHOR]

Undisturbed records of resting stages produced in the past and stored in coastal sediments are very valuable to science, because they may provide unique insights into past evolutionary and ecological trajectories. Within marine phytoplankton, multidecadal time series of monoclonal strains germinated from resting stages have been established for diatoms ( Skeletonema marinoi) and dinoflagellates ( Pentapharsodinium dalei), spanning ca. a century. Phenotypic and genotypic analyses of these time series have revealed effects of past environmental changes on population genetic structure. Future perspectives include direct comparisons of phenotypes and genotypic data of populations, for example, by genomewide assays that can correlate phenotypic trends with genotypes and allele frequencies in temporally separated strains. Besides their usefulness as historical records, 'seed' banks of phytoplankton resting stages also have the potential to provide an inoculum that influences present populations through 'dispersal from the past' (the storage effect) and are important for adaptation to future environments through their standing genetic diversity. [ABSTRACT FROM AUTHOR]

In order to establish a baseline for proxy-based reconstructions for the Young Sound-Tyrolerfjord system (Northeast Greenland), we analysed the spatial distribution of primary production and sea ice proxies in surface sediments from the fjord, against monitoring data from the Greenland Ecosystem Monitoring Programme. Clear spatial gradients in organic carbon and biogenic silica contents reflected marine influence, nutrient availability and river-induced turbidity, in good agreement with in situ measurements. The sea ice proxy IP was detected at all sites but at low concentrations, indicating that IP records from fjords need to be carefully considered and not directly compared to marine settings. The sea ice-associated biomarker HBI III revealed an open-water signature, with highest concentrations near the mid-July ice edge. This proxy evaluation is an important step towards reliable palaeoenvironmental reconstructions that will, ultimately, contribute to better predictions for this High Arctic ecosystem in a warming climate. [ABSTRACT FROM AUTHOR]

We present the first multi-site study of dinoflagellate cyst records spanning ca. AD 1860-2000 from the west Iberian coast. Our aim was to reconstruct environmental changes in the Western Iberia Upwelling Ecosystem, one of the most biologically productive areas in the world, and an active fishery region. A major shift in cyst assemblages was recorded off the northwestern shelf sector between 1920 and 1950 towards autotrophic dominance, and consisted of a multi-fold increase in total cyst concentrations and cysts of Lingulodinium polyedrum, accompanied by an increase in Protoceratium reticulatum cysts. The observed changes pre-date the industrialization of agriculture in Portugal, and are concomitant with a shift in the North Atlantic Oscillation (NAO) towards negative indices (higher river input) and increasing sea-surface temperatures. The southernmost record, with reduced river- and human influence, showed only minor changes during the 20th century. Here, an increase in Protoperidinioid cysts after the 1980s is related to upwelling intensification. Our study indicates that the main changes recorded in the Western Iberian Upwelling system during the 20th century were driven by regional climate variability (warming, increased water stability and nutrient availability), possibly enhanced by anthropogenic nutrient input from the second half of the century. Our results highlight the complexity of the environmental drivers that may act upon dinoflagellate communities within the same region. The 20th-century environmental change in the Western Iberian Ecosystem has resulted in a shift towards marked autotrophic dominance of dinoflagellate cyst communities, and the northward expansion of species associated with Harmful Algal Blooms. [ABSTRACT FROM AUTHOR]

Ribeiro, S., Moros, M., Ellegaard, M. & Kuijpers, A. 2012 (January): Climate variability in West Greenland during the past 1500 years: evidence from a high-resolution marine palynological record from Disko Bay. Boreas, Vol. 41, pp. 68-83. 10.1111/j.1502-3885.2011.00216.x. ISSN 0300-9483. Here we document late-Holocene climate variability in West Greenland as inferred from a marine sediment record from the outer Disko Bay. Organic-walled dinoflagellate cysts and other palynomorphs were used to reconstruct environmental changes in the area through the last c. 1500 years at 30-40 years resolution. Sea ice cover and primary productivity were identified as the two main factors driving dinoflagellate cyst community changes through time. Our data provide evidence for an opposite climate trend in West Greenland relative to the NE Atlantic region from c. AD 500 to 1050. For the same period, sea-surface temperatures in Disko Bay are out-of-phase with Greenland ice-core reconstructed temperatures and marine proxy data from South and East Greenland. This is probably governed by an NAO-type pattern, which results in warmer sea-surface conditions with less extensive sea ice in the area for the later part of the Dark Ages cold period ( c. AD 500 to 750) and cooler conditions with extensive sea ice inferred for the first part of the Medieval Climate Anomaly (MCA) ( c. AD 750 to 1050). After c. AD 1050, the marine climate in Disko Bay becomes in-phase with trends described for the NE Atlantic, reflected in the warmer interval for the remainder of the MCA ( c. AD 1050-1250), followed by cooling towards the onset of the Little Ice Age at c. AD 1400. The inferred scenario of climate deterioration and extensive sea ice is concomitant with the collapse of the Norse Western Settlement in Greenland at c. AD 1350. [ABSTRACT FROM AUTHOR]

The Fram Strait is one of the largest gateways through which meltwater and sea ice are exported to the subarctic North Atlantic, transiting the North-East Greenland shelf via the southward flowing East Greenland Current. Observations indicate a recent freshening of the East Greenland Current that may have implications for wider oceanic circulation regimes. The North-East Greenland shelf is an opportune region to assess these changes back through time. Paleoceanographic reconstructions from the North-East Greenland shelf are sparse and their temporal coverage is limited to the Holocene, limiting our ability to assess the impact of rapid climatic variations on marine conditions, such as during the Younger Dryas/Holocene transition. Here, we present data from a well-dated marine sediment core retrieved from the North-East Greenland shelf (74°N; east of Young Sound-Tyrolerfjord system) that captures the late Younger Dryas Stadial through to the Mid-Holocene at sub-centennial resolution. We apply a multi-proxy approach to reconstruct changes in productivity, surface and bottom ocean conditions. We show that at 74° N the presence of warm Atlantic waters on the inner North-East Greenland shelf was limited to the late Younger Dryas, as the Greenland Ice Sheet retreated landward and isostatic rebound caused the area to uplift. A unique dimension to this record is its location within one of the few biological hotspots on the East Greenland shelf today; the Sirius Water polynya. Archaeological studies indicate the polynya was forming as early as 4500 years ago, but nothing is known about its evolution from a marine perspective. Cooling of bottom waters, increasing sea-surface productivity and more frequent open water conditions indicate an Early Holocene onset of the Sirius Water (ca. 10–8.7 ka BP). • First paleoceanographic study from the Sirius Water polynya on the North-East Greenland shelf. • Multi-proxy approach to reconstruct productivity and bottom water conditions. • Sub-centennial resolution over the Younger Dryas/Holocene transition. • Extensive Atlantic Water influence during the late Younger Dryas. • Indications of recurrent Sirius Water Polynya formation since the Early Holocene (∼10–8.7 ka BP). [ABSTRACT FROM AUTHOR]

The accelerating sea-ice, ice sheet and glacial melt associated with climate warming have resulted in important changes in the Arctic region over the past decades. In northern Baffin Bay, the formation of the North Open Water (NOW) polynya, which is intrinsically linked to regional sea-ice conditions and ocean circulation, has become more variable in recent years. To understand how climate-driven changes affect sea-surface conditions in the polynya, we analyzed dinoflagellate cyst assemblages from a sediment core record that covers the past ca. 3800 years, and developed an index based on the locations of modern analogues from a large regional reference dataset. Our results suggest a prolonged open-water season characterized by higher summer sea-surface salinity and temperature between ca. 3800 to 2500 years BP, followed by gradual cooling, freshening and increased sea-ice influence from 2500 to 1500 years BP, and continued sea-surface cooling with a shorter open-water season from 1500 to 156 years BP. The modern warming translates into a rapid turnover in the composition of dinoflagellate cyst assemblages during the last 50 years of our record, unprecedented for at least the past 3800 years studied here. For the uppermost part of our core (ca. 2009 to 2015 CE), the dinoflagellate cyst assemblages suggest increased stratification and sea-surface freshening resulting from increased glacial runoff and Arctic sea-ice export into the NOW region. Arctic climate projections indicate accelerated sea-ice thinning and ice sheet melt in the future, pointing to a shorter polynya season and increased polar inflows leading to fundamental changes within the NOW polynya into future years. • Long-term subdecadal to multidecadal record of summer sea-surface conditions using dinoflagellate cysts in the North Water Polynya. • Development of an index based on the locations of modern assemblage analogues to assess changes to polynya dynamics. • Sea-surface cooling and freshening from ca. 2200 years to 156 years BP. • Late Holocene record shows no comparable analogue to the last ca. 50 years. [ABSTRACT FROM AUTHOR]