Diatom-based reconstructions of climate and ocean conditions from Svalbard and Baffin Bay since the Last Glacial Maximum

The ongoing climate warming has a profound impact on the sensitive Arctic region and the recent changes in Arctic environment have an alarming rate and magnitude. To better understand the changes taking place in the Arctic region, and to project the future impacts of the ongoing climate change, we need to have records of past climate conditions and past interactions between climate system components, which can be obtained using marine proxy records. This work examines ocean surface conditions from high northern latitudes after the Last Glacial Maximum using marine fossil diatom assemblages. Long-term paleoclimatic and -oceanographic records are obtained from northern Svalbard and central-eastern Baffin Bay using quantitative and qualitative diatom analyses, and sediment grain size distribution analysis. An additional focus of this work was to study the ecology of common northern North Atlantic diatom species and define their relationship to environmental variables (aSSTs and sea ice) in order to identify the best indicator species for these environmental variables and to improve their reliability as paleoceanographic indicators. The Baffin Bay study site was investigated for the deglacial period (10−14 kyr BP), and the results suggest a warmer ocean surface in central-eastern Baffin Bay during the cold Younger Dryas period (11.7−12.9 kyr BP) indicating that the ocean was out of phase with atmospheric conditions over Greenland. The warmer conditions were caused by enhanced inflow of Atlantic-sourced waters and increased solar insolation on the Northern Hemisphere, which amplified seasonality over Baffin Bay and had a significant role triggering the ice margin in West Greenland. The paleoceanographic record from northern Svalbard represents the late Holocene (last ca. 4 200 years), and the results show a clear climate shift at 2.5 kyr BP, as the study location changed from stable, glacier-proximal conditions into fluctuating glacier-distal conditions, emphasizing the sensitivity of the Arctic environment to climate oscillations. Understanding diatom species` relationship to environmental variables is essential and this work identifies robust indicators for cold, temperate and warm waters and for sea ice. The results show that not all sea ice-associated species have a statistically significant relationship to sea ice. While this species is often found in sea ice and in the marginal ice zone, its ecology appears to be more complex. The paleoceanographic and –climatic records in this work give new insights to our current knowledge of past climate variability, and reform some of our current understanding of the past climate conditions on a local scale. This work also improves the applicability of the key northern North Atlantic diatom taxa as paleo-indicators, questioning previous knowledge on the ecology of some species and highlighting some important taxonomic issues.Viimeaikaiset muutokset arktisessa ympäristössä ovat tapahtuneet hälyttävällä nopeudella ja intensiteetillä, sillä arktinen alue on herkkä ilmaston vaihteluille. Tutkimalla menneitä ilmasto-olosuhteita sekä vuorovaikutuksia ilmastosysteemin komponenttien välillä, voidaan paremmin ymmärtää nykyisiä muutoksia arktisessa ympäristössä sekä arvioida tulevia ilmastonmuutoksen vaikutuksia. Merenpohjan sedimenttisarjat tarjoavat epäsuoraa tietoa menneistä pitkän aikavälin ilmastonvaihteluista sekä meren pintaveden olosuhteiden muutoksista. Jäätikön reunan läheisyydestä saatavan tiedon avulla pystytään tutkimaan muinaisia meren ja jäätikön välisiä vuorovaikutuksia, mikä on erittäin tärkeä ymmärtää arvioitaessa nykyisen meren pintaveden lämpenemisen vaikutuksia Grönlannin mereen päättyviin jäätikköihin. Tässä työssä tutkitaan edellisen jääkauden jälkeisiä merenpinnan olosuhteiden (meriveden pintalämpötilan, merijään ja merivirtojen) vaihteluita Pohjois-Huippuvuorilta sekä Baffininlahdelta käyttäen piileväyhteisöjä. Työssä käytetään piileväyhteisöihin perustuvia kvantitatiivisiä ja kvalitatiivisia metodeja, sekä sedimentin raekoko-analyysiä. Työssä tutkitaan myös yleisempien pohjoisella Pohjois-Atlantilla esiintyvien piilevien ekologiaa sekä vasteita yleisimpiin ympäristömuuttujiin; meriveden pintalämpötilaan ja merijäähän. Lajikohtaisia ympäristövasteita tutkimalla pyritään selvittämään parhaimmat indikaattorilajit tutkituille ympäristömuuttujille sekä edistämään lajien käyttömahdollisuuksia paleotutkimuksissa. Baffininlahdelta tutkittiin deglasiaation aikaisia (10 000−14 000 vuotta sitten) muutoksia. Tulokset osoittavat että meren pintavedet olivat lämpimiä kylmän Nuorempi Dryas-kauden aikana (11 700−12 900 vuotta sitten), mikä viittaa siihen että meren pintaosien olosuhteet poikkesivat Grönlannissa vallinneista ilmasto-olosuhteista. Nämä lämpimät olosuhteet aiheutuivat alueella lisääntyneestä Atlanttisesta merivirtauksesta sekä pohjoisella pallonpuoliskolla lisääntyneestä auringon säteilystä. Lämpimällä merivedellä oli suuri vaikutus Länsi-Grönlannissa sijaitsevan Jakobshavn Isbræ-jäätikkövirran romahtamiseen. Pohjois-Huippuvuorilta tutkittu sedimenttisarja kattaa noin viimeisen 4 200 vuoden ajanjakson. Tuloksien perusteella Pohjois-Huippuvuorilla tapahtui merkittävä muutos noin 2 500 vuotta sitten kun ilmasto vaihtui melko tasaisesta hyvin vaihtelevaksi samalla kun alueella sijainnut jäätikkö vetäytyi tutkimusalueen läheisyydestä kauemmaksi. Koska piileviä käytetään indikkaattoreita paleoilmastotutkimuksissa, on erityisen tärkeää tuntea piilevien ekologiaa ja lajikohtaisia vasteita ympäristömuuttujiin. Tutkimus piilevien lajikohtaisista ympäristövasteista ja ekologiasta jakaa lajit kylmän-, lämpimän- ja lauhkeanveden indilaattoreiksi sekä merijää-indikaattoreiksi. Tutkimus osoittaa että kaikilla merijäähän yhdistetyillä lajeilla ei ole tilastollisesti merkittävää suhdetta merijäähän, osoittaen että näiden lajien ekologia on luultua monimutkaisempi. Kokonaisuudessaan työ esittelee menneitä meren pintaosissa ja ilmastossa tapahtuneita vaihteluita, mikä lisää ymmärrystämme ja uudistaa joitakin aiempia käsityksiämme menneistä paikallisista ilmastonvaihteluista. Lisäksi tutkimus vahvistaa nykyistä tietämystämme Pohjois-Atlantin piilevälajiston ympäristövasteista, mutta myös kyseenalaistaa joidenkin lajien nykyistä käyttöä indikaattoreina paleotutkimuksissa, sekä tuo esiin taksonomisia ongelmia jotka vaativat selvitystä tulevaisuudessa, sillä ne voivat mahdollisesti vääristää tulkintoja ja aiheuttaa virheellisiä ilmastorekonstruktioita

The biogeography and ecology of common diatom species in the northern North Atlantic, and their implications for paleoceanographic reconstructions

Sound knowledge of present-day diatom species and their environments is crucial when attempting to reconstruct past climate and environmental changes based on fossil assemblages. For the North Atlantic region, the biogeography and ecology of many diatom taxa that are used as indicator-species in paleoceanographic studies are still not well known. Using information contained in large diatom-environment calibration datasets can greatly increase our knowledge on diatom taxa and improve the accuracy of paleoenvironmental reconstructions. A diatom calibration dataset including 183 surface sediment samples from the northern North Atlantic was used to explore the distribution and ecology of 21 common Northern Hemisphere diatom taxa. We define the ecological responses of these species to April sea ice concentrations and August sea surface temperatures (aSSTs) using Huisman-Olff-Fresco (HOF)-response curves, provide distribution maps, temperature optima and ranges, and high-quality light microscope images. Based on the results, we find species clearly associated with cold, warm and temperate waters. All species have a statistically significant relationship with aSST, and 15 species with sea ice. Of these, Actinocyclus curvatulus, Fragilariopsis oceanica and Porosira glacialis are most abundant at high sea ice concentrations, whereas Coscinodiscus radiants, Shionodiscus oestrupii, Thalassionema nitzschioides, Thalassiosira angulata, Thalassiosira nordenskioeldii and Thalassiosira pacifica are associated with low sea ice concentrations/ice-free conditions. Interestingly, some species frequently used as sea ice indicators, such as Fragilariopsis cylindrus, show similar abundances at high and low sea ice concentrations with no statistically significant relationship to sea ice.Peer reviewe

Invertebrate communities of the High Arctic ponds in Hornsund

How environmental conditions influence current distributions of organisms at the local scale in sensitive high Arctic freshwaters is essential to understand in order to better comprehend the cascading consequences of the ongoing climate change. This knowledge is also important background data for paleolimnological assessments of long-term limnoecological changes and in describing the range of environmental variability. We sampled five limnologically different freshwater sites from the Fuglebergsletta marine terrace in Hornsund, southern Svalbard, for aquatic invertebrates. The invertebrate communities were tested against non-climatic environmental drivers (limnological and catchment variables). A clear separation in the communities between the sites was observed. The largest and deepest lake was characterized by a diverse Chironomidae community but Cladocera were absent. In a pond with marine influence, crustaceans, such as Ostracoda, Amphipoda, and calanoid Copepoda were the most abundant invertebrates. Two nutrient-rich ponds were dominated by a chironomid, Orthocladius consobrinus, whereas the most eutrophic pond was dominated by the cladoceran Daphnia pulex suggesting decreasing diversity along with the trophic status. Overall, nutrient related variables appeared to have an important influence on the invertebrate community composition and diversity, the trophic state of the sites being linked with their exposure to geese guano. Other segregating variables included water color, presence/absence of fish, abundance of aquatic vegetation and lake depth. These results suggest that since most of these variables are climate-driven at a larger scale, the impacts of the ongoing climate change will have cumulative effects on aquatic ecosystems.How environmental conditions influence current distributions of organisms at the local scale in sensitive High Arctic freshwaters is essential to understand in order to better comprehend the cascading consequences of the ongoing climate change. This knowledge is also important background data for paleolimnological assessments of long-term limnoecological changes and in describing the range of environmental variability. We sampled five limnologically different freshwater sites from the Fuglebergsletta marine terrace in Hornsund, southern Svalbard, for aquatic invertebrates. Invertebrate communities were tested against non-climatic environmental drivers as limnological and catchment variables. A clear separation in the communities between the sites was observed. The largest and deepest lake was characterized by a diverse Chironomidae community but Cladocera were absent. In a pond with marine influence, crustaceans, such as Ostracoda, Amphipoda, and calanoid Copepoda were the most abundant invertebrates. Two nutrient-rich ponds were dominated by a chironomid, Orthocladius consobrinus, whereas the most eutrophic pond was dominated by the cladoceran Daphnia pulex, suggesting decreasing diversity along with the trophic status. Overall, nutrient related variables appeared to have an important influence on the invertebrate community composition and diversity, the trophic state of the sites being linked with their exposure to geese guano. Other segregating variables included water color, presence/absence of fish, abundance of aquatic vegetation and lake depth. These results suggest that since most of these variables are climate-driven at a larger scale, the impacts of the ongoing climate change will have cumulative effects on aquatic ecosystems.Peer reviewe

Sedimentary environment, lithostratigraphy and dating of sediment sequences from Arctic lakes Revvatnet and Svartvatnet in Hornsund, Svalbard

Peer reviewe

Younger Dryas ice margin retreat triggered by ocean surface warming in central-eastern Baffin Bay

The transition from the last ice age to the present-day interglacial was interrupted by the Younger Dryas (YD) cold period. While many studies exist on this climate event, only few include high-resolution marine records that span the YD. In order to better understand the interactions between ocean, atmosphere and ice sheet stability during the YD, more high-resolution proxy records from the Arctic, located proximal to ice sheet outlet glaciers, are required. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from central-eastern Baffin Bay, covering the period 14.0-10.2 kyr BP. Our record reveals warmer sea surface conditions and strong interactions between the ocean and the West Greenland ice margin during the YD. These warmer conditions were caused by increased Atlantic-sourced water inflow combined with amplified seasonality. Our results emphasize the importance of the ocean for ice sheet stability under the current changing climate.Peer reviewe

Historical human impact on Productivity and biodiversity in a subalpine oligotrophic lake in Scandinavia

We conducted a paleolimnological study to examine how changes in human activity interacted with climate to influence productivity and biodiversity over the past millennium in oligotrophic Lake Atnsjøen, SE Norway. The study included analyses of sediment geochemistry, subfossil diatoms and cladocerans, and macrofossils. Results were compared with the historical record of human activities in the catchment, pollen analysis and paleoclimate inferences from the lake. During the first 750 years of the record (1000–1750 CE), a time of relatively low human activity, lake productivity and biodiversity were strongly related to climate. During the Little Ice Age (1550–1800 CE), lake productivity and diatom diversity were constrained by cold climate. A Century of climate warming (1780–1880 CE) initiated an increase in productivity. Accelerated human settlement after 1850 CE, however, had an even stronger impact on productivity, mediated by increased agriculture and/or forestry, which led to greater nutrient loading of the lake. Similarly, diatoms in the lake responded to the rise in temperature, but increasing human activity also had a moderate impact on the diatom community, which displayed weak signs of nutrient enrichment. From 1980 to 1990 CE onwards, lake productivity declined as a consequence of a recent decrease in human activity and changing land use. The human-induced increase in lake productivity starting ca. 1850 CE propagated through the food web and increased consumer productivity, as reflected by greater accumulation rates of cladocerans, trichopterans and turbellarians. The cladoceran community was likely under top-down control of fish, as indicated by changes in size structure and diversity. Our study showed that increasing human activity during the settlement period had a stronger impact on lake productivity than did climate. Furthermore, the slight human-mediated increase in nutrient loading had different impacts on productivity and biodiversity in the study lake. This study demonstrates that even relatively small changes in human activities in watersheds can have measurable impacts on nutrient-poor lakes.acceptedVersio

Mid to late-Holocene sea-surface temperature variability off north-eastern Newfoundland and its linkage to the North Atlantic Oscillation

In recent decades the surface water temperature and salinity in the Labrador Sea have been influenced by atmospheric circulation patterns, such as the North Atlantic Oscillation (NAO), as well as a trend to increasingly warm atmospheric temperatures in recent years. These changes are concerning, given the important role that temperature and salinity have on deep convection in the Labrador Sea. Yet, due to the shortness of available records, the long-term patterns of climate variability in the region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1-2 degrees C. Long-term cooling was likely the result of declining Northern Hemisphere orbital summer insolation, potentially amplified by long-term changes in surface and bottom water salinity, which led to a gradual reduction in the stratification of the water column. Centennial fluctuations in temperature vary in-phase with reconstructed variations in the NAO, supporting a consistent relationship between atmospheric circulation and SST over centennial-millennial timescales. Other factors influencing the SST variability may have been solar forcing during the mid-Holocene and variations in the strength of the subpolar gyre during the late-Holocene. The most prolonged cool period at 5.2-4.1 cal ka BP coincides with sharply reduced salinity in the Labrador Sea and a weakening of deep ventilation in the northeast Atlantic, highlighting a period with altered ocean surface conditions and circulation across the northern North Atlantic

Diatom percentage abundances and sea surface temperature reconstruction for core AI07-06G, from Trinity Bay, Newfoundland

Due to the shortness of available records, the longterm patterns of climate variability in the Labrador Sea and Newfoundland region are not clear. Here, a diatom-based reconstruction of summer sea-surface temperature (SST) developed from Trinity Bay, Newfoundland, provides insight into variations of SST since 7.2 cal ka BP in the southwestern Labrador Sea. The results show that the Holocene Thermal Maximum (HTM) lasted until c. 5.2 cal ka BP, which was followed by a gradual cooling trend overprinted by centennial temperature fluctuations of 1-2°C

Sedimentary environment, lithostratigraphy and dating of sediment sequences from Arctic lakes Revvatnet and Svartvatnet in Hornsund, Svalbard

The sedimentary environment, sediment characteristics and age-depth models of sediment sequences from Arctic lakes Revvatnet and Svartvatnet, located near the Polish Polar Station in Hornsund, southern Svalbard (77°N), were studied with a view to establishing a basis for paleolimnological climate and environmental reconstructions. The results indicate that catchment-to-lake hydroclimatic processes probably affect the transportation, distribution and accumulation of sediments in different parts of lakes Revvatnet and Svartvatnet. Locations with continuous and essentially stable sedimentary environments were found in both lakes between water depths of 9 and 26 m. We used several different dating techniques, including 137Cs, 210Pb, AMS 14C, and paleomagnetic dating, to provide accurate and secured sediment chronologies. Arecovered sequence from the northern basin of Revvatnet spans more than one thousand years long with laminated stratigraphy in the upper part of the sediment. Based on AMS 14C dates, it is possible to suppose that Revvatnet basin was not occupied by a valley glacier during the Little Ice Age. The dates were supported by 137Cs chronologies, but not confirmed with other independent dating methods that extent beyond the last 50 years. A sedimentary sequence from the northern basin of Svartvatnet provides a potential archive for the study of climate and environmental change for the last ca. 5000 years. Based on the stratigraphy and a Bayesian age-depth model of AMS14C and paleosecular variation (PSV) dates, the recovered sediment sections represent a continuous and stable sedimentation for the latter half of the Holocene