Hundred years of genetic structure in a sediment revived diatom population.

This paper presents research on the genetic structure and diversity of populations of a common marine protist and their changes over time. The bloom-forming diatom Skeletonema marinoi was used as a model organism. Strains were revived from anoxic discrete layers of a (210)Pb-dated sediment core accumulated over more than 100 y, corresponding to >40,000 diatom mitotic generations. The sediment core was sampled from the highly eutrophic Mariager Fjord in Denmark. The genetic structure of S. marinoi was examined using microsatellite markers, enabling exploration of changes through time and of the effect of environmental fluctuations. The results showed a stable population structure among and within the examined sediment layers, and a similar genetic structure has been maintained over thousands of generations. However, established populations from inside the fjord were highly differentiated from open-sea populations. Despite constant water exchange and influx of potential colonizers into the fjord, the populations do not mix. One fjord population, accumulated in 1980, was significantly differentiated from the other groups of strains isolated from the fjord. This differentiation could have resulted from the status of Mariager Fjord, which was considered hypereutrophic, around 1980. There was no significant genetic difference between pre- and posteutrophication groups of strains. Our data show that dispersal potential and generation time do not have a large impact on the genetic structuring of the populations investigated here. Instead, the environmental conditions, such as the extreme eutrophication of the Mariager Fjord, are deemed more important.

Sediment discharge from Greenland's marine-terminating glaciers is linked with surface melt.

Sediment discharged from the Greenland Ice Sheet delivers nutrients to marine ecosystems around Greenland and shapes seafloor habitats. Current estimates of the total sediment flux are constrained by observations from land-terminating glaciers only. Addressing this gap, our study presents a budget derived from observations at 30 marine-margin locations. Analyzing sediment cores from nine glaciated fjords, we assess spatial deposition since 1950. A significant correlation is established between mass accumulation rates, normalized by surface runoff, and distance down-fjord. This enables calculating annual sediment flux at any fjord point based on nearby marine-terminating outlet glacier melt data. Findings reveal a total annual sediment flux of 1.324 + /- 0.79 Gt yr-1 over the period 2010-2020 from all marine-terminating glaciers to the fjords. These estimates are valuable for studies aiming to understand the basal ice sheet conditions and for studies predicting ecosystem changes in Greenland's fjords and offshore areas as the ice sheet melts and sediment discharge increase.

Abundance and sources of plastic debris on beaches in a plastic hotspot, Nha Trang, Viet Nam.

Viet Nam is challenged by extensive marine plastic pollution, however, remediation efforts are hampered by undefined sources to the coastal environment. This study surveyed the abundance, type, and source of beached plastic litter at seven beaches along the coast of Nha Trang, Viet Nam. A total of 4754 beached plastic litter items (>2 cm) yielded a mean abundance of 19.8 ± 19.5 items m-2 corresponding to 116 ± 226 g DW m-2. Our results demonstrate that plastic litter related to fishing and aquaculture constituted at least 62 % of the total by weight and 38 % by number, showing that these two sectors are responsible for a significant part of the plastic pollution along the coast. Hence, we argue that improved management of the fishing and aquaculture sectors could substantially reduce marine plastic pollution along Viet Nam's coast.

Holocene polynya dynamics and their interaction with oceanic heat transport in northernmost Baffin Bay.

Baffin Bay hosts the largest and most productive of the Arctic polynyas: the North Water (NOW). Despite its significance and active role in water mass formation, the history of the NOW beyond the observational era remains poorly known. We reconcile the previously unassessed relationship between long-term NOW dynamics and ocean conditions by applying a multiproxy approach to two marine sediment cores from the region that, together, span the Holocene. Declining influence of Atlantic Water in the NOW is coeval with regional records that indicate the inception of a strong and recurrent polynya from ~ 4400 yrs BP, in line with Neoglacial cooling. During warmer Holocene intervals such as the Roman Warm Period, a weaker NOW is evident, and its reduced capacity to influence bottom ocean conditions facilitated northward penetration of Atlantic Water. Future warming in the Arctic may have negative consequences for this vital biological oasis, with the potential knock-on effect of warm water penetration further north and intensified melt of the marine-terminating glaciers that flank the coast of northwest Greenland.

Vulnerability of the North Water ecosystem to climate change.

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.

Defining ecological reference conditions in naturally stressed environments - How difficult is it?

The present study performed in Horten Inner Harbor (southern Norway) shows that foraminifera link the present-day Ecological Quality Status (EcoQS) to EcoQS of former times and, this way, bridge an important knowledge gap concerning determination of reference conditions, even in naturally stressed environments such as transitional waters and oxygen depleted habitats. In Horten Inner Harbor, geochemical data in the oldest deposits showed stable background concentrations for about 200 years (from about 1600 to 1800) before human activity became noteworthy, reflecting 'good' to 'high' status. Hence, it is reasonable that organisms, which lived in the area during the same nearly un-impacted time interval, represent the biologically defined reference conditions, irrespectively of whether the biotic indices are classified as 'good' or 'bad'. The present paper illustrates, with a conceptual model, how the retrospective foraminiferal biomonitoring method can be used to detect environmental perturbations in estuaries and meet the difficulties of the Estuarine Quality Paradox.

Resuspension and settling of helminth eggs in water: Interactions with cohesive sediments.

Helminth parasite eggs in low quality water represent main food safety and health hazards and are therefore important indicators used to determine whether such water can be used for irrigation. Through sedimentation helminth eggs accumulate in the sediment, however resuspension of deposited helminth eggs will lead to increased concentration of suspended eggs in the water. Our study aimed to determine the erodibility (erosion rate and erosion threshold) and settling velocity of Ascaris and Trichuris eggs as well as cohesive sediment at different time points after incorporation into the sediment. Cohesive sediment collected from a freshwater stream was used to prepare a sediment bed onto which helminth eggs were allowed to settle. The erodibility of both sediment and helminth eggs was found to decrease over time indicating that the eggs were incorporated into the surface material of the bed and that this material was stabilized through time. This interaction between eggs and bulk sediment was further manifested in an increased settling velocity of suspended eggs when sediment was present in the suspension as compared to a situation with settling in clean water. The incorporation into the sediment bed and the aggregation with sediment particles decrease the mobility of both helminth egg types. Our findings document that helminth eggs should not be viewed as single entities in water systems when modelling the distribution of eggs since both erodibility and settling velocity of eggs are determined by mobility of the sediment present in the water stream. Recalculation of the erosion threshold for helminth eggs and sediment showed that even at relatively low current velocities i.e. 0.07-0.12ms(-1) newly deposited eggs will be mobile in open irrigation channels. These environmental factors affecting resuspension must be taken into account when developing models for sedimentation of helminth eggs in different water systems.

Sedimentation of helminth eggs in water.

Helminth parasite eggs in low quality water represent health risks when used for irrigation of crops. The settling velocities of helminth eggs (Ascaris suum, Trichuris suis, and Oesophagostomum spp.) and wastewater particles were experimentally determined in tap water and in wastewater using Owen tubes. The settling velocities of eggs in tap water was compared with theoretical settling velocities calculated by Stoke's law using measurements of size and density of eggs as well as density and viscosity of tap water. The mean settling velocity in tap water of 0.0612 mm s(-1) found for A. suum eggs was significantly lower than the corresponding values of 0.1487 mm s(-1) for T. suis and 0.1262 mm s(-1) for Oesophagostomum spp. eggs. For T. suis and Oesophagostomum spp. eggs the theoretical settling velocities were comparable with the observed velocities in the Owen tubes, while it was three times higher for A. suum eggs. In wastewater, the mean settling velocity for A. suum eggs (0.1582 mm s(-1)) was found to be different from T. suis (0.0870 mm s(-1)), Oesophagostomum spp. (0.1051 mm s(-1)), and wastewater particles (0.0474 mm s(-1)). This strongly indicates that in low quality water the eggs are incorporated into particle flocs with different settling velocities and that the settling velocity of eggs and particles is closely associated. Our results document that there is a need to differentiate the sedimentation of different types of helminth eggs when assessing the quality of low quality water, e.g. for irrigation usage. The results can also be used to improve existing models for helminth egg removal.

Phytoplankton growth after a century of dormancy illuminates past resilience to catastrophic darkness.

Photosynthesis evolved in the oceans more than 3 billion years ago and has persisted throughout all major extinction events in Earth's history. The most recent of such events is linked to an abrupt collapse of primary production due to darkness following the Chicxulub asteroid impact 65.5 million years ago. Coastal phytoplankton groups (particularly dinoflagellates and diatoms) appear to have been resilient to this biotic crisis, but the reason for their high survival rates is still unknown. Here we show that the growth performance of dinoflagellate cells germinated from resting stages is unaffected by up to a century of dormancy. Our results clearly indicate that phytoplankton resting stages can endure periods of darkness far exceeding those estimated for the Cretaceous-Paleogene extinction and may effectively aid the rapid resurgence of primary production in coastal areas after events of prolonged photosynthesis shut-down.

Sedimentation and chronology of heavy metal pollution in Oslo harbor, Norway.

Stratigraphic profiles of Cu, Cd and Hg in ten sediment cores from the Oslo harbor, Norway, combined with results of radiometric dating demonstrate that pollution by these metals peaked between 1940 and 1970. Dating results indicate that Hg discharges peaked between 1940 and 1950, Cd reached maximum ca. 1955-1960, and Cu has the highest concentration in sediment interval corresponding to ca. 1970. Geochemical profiles and maxima of Cu, Cd and Hg concentrations can be used as chronostratigraphic markers for sediment cores from the Oslo harbor. Acoustic backscatter and sediment core data indicate that propeller wash affects the seabed in the Oslo harbor. The propeller-induced turbulence causes erosion, and in places exposes and remobilizes contaminated sediments that accumulated in the harbor during previous decades. Such re-exposure of contaminated sediments could be detrimental to local ecosystems and offset remediation efforts, warranting further impact studies and potential mitigation strategies to prevent redistribution.