Seasonal methane and carbon dioxide emissions from the coastal nearshore of the Kolyma river, Siberia.

<p>Arctic rivers deliver ≈11% of global river discharge into the Arctic Ocean, while this ocean represents only ≈1% of the global ocean volume. Ongoing climate warming across the Arctic, and specifically Siberia, has led to regional-scale changes in precipitation patterns, greater rates of permafrost thaw and active layer deepening, as well as enhanced riverbank and coastal erosion. Combined, these climatic and cryospheric perturbations have already resulted in increased freshwater discharge and changes to constituent loads (e.g. dissolved organic carbon - OC) supplied from land to the Arctic Ocean.</p><p>To date, the majority of studies examining terrestrial organic matter (OM) delivery to the Arctic Ocean have focused almost entirely on freshwater (riverine) or fully-marine environments and been conducted during late summer seasons – often due to logistical constraints. Despite this, an improved understanding of how OC is transformed, mineralised and released during transit through the highly reactive nearshore estuarine environment is critical for examining the fate and influence of terrestrial OM on the Arctic Ocean. Capturing seasonality over the open water period is also necessary to identify current OM fluxes to the ocean vs the atmosphere, and aid in constraining how future changes may modify them.</p><p>Here we focus upon carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>) measurements collected during six repeated transects of the Kolyma River and nearshore zone (covering ~120 km) from 2019. Transects spanned almost the entirety of the riverine open water season (June to September). We use these results, in parallel with gas concentrations derived from prior studies, to develop and validate a simple box-model of gas emissions from the nearshore zone.</p><p>Observations and model‐derived output data reveal that more than 50% of the cumulative gross delivery of CH<sub>4</sub> and CO<sub>2</sub> to the coastal ocean occurred during the freshet period with dissolved CH<sub>4</sub> concentrations in surface water reaching 660 Nanomole per liter [nmol/l]. These results demonstrate the relevance of seasonal dynamics and its spatial variability which are needed in order to estimate greenhouse gas fluxes on an annual basis.</p><p>More accurate understanding of land-ocean carbon fluxes in the Arctic is therefore crucial to mitigate the effects of climate change and to support the decisions of policy makers.</p>

The effect of repeated sand nourishments on long-term nearshore evolution: a case study for Noordwijk aan Zee, the Netherlands

<p>Sand nourishments are carried out along numerous sandy coasts worldwide to counteract coastal erosion, with the sand added to the inter- and supratidal beach or to the subtidal nearshore profile. Since the early 1990s beach and shoreface nourishments have been carried out along the Dutch coast, with a total nourished volume of 10 to 15 Mm<sup>3</sup>/year. Although we have a reasonable understanding of how an individual nourishment temporarily affects the evolution of nearshore morphology, it is not clear how repeated nourishments influence the long-term dynamics of the nearshore zone. This understanding is crucial, not only for the safety of beachgoers or marine life, but especially in view of the expected increase in the number of nourishments and total nourishment volume given expected accelerating sea-level rise in the decades to come.</p><p>This contribution aims to analyse how repeated nourishments affect the long-term evolution of the shoreline and the two subtidal sandbars at the Dutch beach town Noordwijk aan Zee using Argus video imagery available since 1995. Between 1998 and 2014 four shoreface and three beach nourishments were carried out at the study site. The low-tide time-exposure images of the Argus station were used to determine  sandbar and shoreline position along a 6-km stretch of coast.<br>The results show that prior to the first nourishment the sandbars migrated seaward slowly but persistently. The repeated nourishments permanently decreased this seaward directed migration rate of the sandbars to only a few m/year. The sandbars showed alternating periods of seasonal to multi-year onshore and offshore migration superimposed on this very weak decadal offshore trend. Furthermore, the various sand nourishments gave rise to forked shoreline-sandbar morphology. This large-scale alongshore variability was undone within 1 – 2 years by switches, in which the landward part of a sandbar or the shoreline on one side of the fork realigned with the seaward part of a bar on the other side. These switches appear to be a direct consequence of the repeated nourishments. For example, the 2013-2014 sequence of a beach and a shoreface nourishment resulted in 4 bar switches within the subsequent 2 years, compared to a total of 12 switches in the total dataset of 24.8 years. Further analysis will focus on the effect of repeated nourishments on the temporal and spatial persistence of rip-channel morphology and on the wave conditions that caused the forked morphology to switch.</p>

Dolichospermum lemmermannii (Nostocales) bloom in world s deepest Lake Baikal (East Siberia): abundance, toxicity and factors influencing growth

Mass development of the cyanobacteria Dolichospermum (D. lemmermannii as the dominant species) was reported in the coastal zone of Bol shye Koty Bay (western coast of the southern basin), towards the end of July to the beginning of August in 2019. Blooms were observed as 1 1.5-m wide bands adjoining the shoreline and stretched uninterrupted over 2 km. Abundance of cyanobacteria in blooms varied within 7.2 71.9 thousand cell mL-1, with 0.73 7.20 g m-3 biomass attained. Maximal concentration was observed opposite the biological station of Irkutsk State University, a frequently visited place that was hosting participants of several conferences at that time. Hydrochemical analysis of samples collected four days after continuous heavy rains showed much higher concentrations of nutrients in contrast with the data obtained a week before (24 July), which is normal for that season. Nutrient concentrations were elevated relative to long term averages by 3 to 30 fold: with phosphate concentrations up to 0.200 mg L-1, ammonium ions 0.29 mg L-1, and nitrates 0.31 mg L-1. Possible reasons for the harmful freshwater cyanobacterial bloom that is unusual for this part of the lake are discussed. Excessive proliferation of common cyanobacteria D. lemmermannii in the open lake areas was affected by several factors: long-lasting heavy rains, zero wind, high air (from 13 15 at night to 29 in daytime) and water temperatures (from 15 to 19.2 ); and absence of isolated septic tanks in the nearshore zone.

NUMERICAL SIMULATION OF WAVE-DRIVEN FLOWS ON A MORPHOLOGICALLY EVOLVING BEACH

Wave-driven flows in the nearshore zone are responsible for the erosion and transport of beach sediments, causing a continuous cycle of bathymetric change that is linked with changes to wave transformation and nearshore hydrodynamics. Numerical models have been used to investigate the evolving nearshore wave field corresponding to beach morphology change in field studies (e.g., Ruiz de Alegria-Arzaburu et al., 2013). In the present study, the non-hydrostatic wave-flow SWASH model (Zijlema et al., 2011) is applied to five laboratory cases to investigate the change in wave and flow fields corresponding to evolving beach morphology during a simulated storm event.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/LZQQuuiqsPY