Living on Cold Substrata: New Insights and Approaches in the Study of Microphytobenthos Ecophysiology and Ecology in Kongsfjorden

Organisms in shallow waters at high latitudes are under pressure due to climate change. These areas are typically inhabited by microphytobenthos (MPB) communities, composed mainly of diatoms. Only sparse information is available on the ecophysiology and acclimation processes within MPBs from Arctic regions. The physico-chemical environment and the ecology and ecophysiology of benthic diatoms in Kongsfjorden (Svalbard, Norway) are addressed in this review. MPB biofilms cover extensive areas of sediment. They show high rates of primary production, stabilise sediment surfaces against erosion under hydrodynamic forces,and affect the exchange of oxygen and nutrients across the sediment-water interface. Additionally, this phototrophic community represents a key component in the functioning of the Kongsfjorden trophic web, particularly as a major food source for benthic suspension- or deposit-feeders. MPB in Kongsfjorden is confronted with pronounced seasonal variations in solar radiation, low temperatures, and hyposaline (meltwater) conditions in summer, as well as long periods of ice and snow cover in winter. From the few data available, it seems that these organisms can easily cope with these environmental extremes. The underlying physiological mechanisms that allow growth and photosynthesis to continue under widely varying abiotic parameters, along with vertical migration and heterotrophy, and biochemical features such as a pronounced fatty-acid metabolism and silicate incorporation are discussed. Existing gaps in our knowledge of benthic diatoms in Kongsfjorden, such as the chemical ecology of biotic interactions, need to be filled. In addition, since many of the underlying molecular acclimation mechanisms are poorly understood, modern approaches based on transcriptomics, proteomics, and/or metabolomics, in conjunction with cell biological and biochemical techniques, are urgently needed. Climate change models for the Arctic predict other multifactorial stressors, such as an increase in precipitation and permafrost thawing, with consequences for the shallow-water regions. Both precipitation and permafrost thawing are likely to increase nutrient-enriched, turbid freshwater runoff and may locally counteract the expected increase in coastal radiation availability. So far, complex interactions among factors, as well as the full genetic diversity and physiological plasticity of Arctic benthic diatoms, have only rarely been considered. The limited existing information is described and discussed in this review

Assessment of periglacial response to increased runoff: An Arctic hydrosystem bears witness

International audienceIn the general context of global warming, the cryosphere appears as an environment that exhibits a strong sensitivity to climate variations. Overall, glacier systems are now known to be reliable indicators of climate trends. Although glacier dynamics are subject to international monitoring networks, periglacial environments are much less observed. However, these newly deglaciated areas get wider since glaciers are retreating, and their dynamics become increasingly significant. The observed increase in water fluxes, temperature and precipitation, permafrost melting, and reduced cold periods induce a combined control on modifications of the glacier and periglacial dynamics. Such consequences are also visible on the landscape, hinting at an adaptation of the environment to the climatic forcing.The work carried out focuses on Austre Lovénbreen area, a small 10‐km2 glacier basin (Svalbard, 78.87°N, 12.15°E, west coast of Spitsbergen) exhibiting typical arctic glacial retreat trends. Its geomorphological characteristics as well as its observatory status make it an appropriate control area. Our investigations are based on a combination of classical on‐site snow, ice, and geomorphological measurements, combined with innovative methods using aerial photography (e.g., from unmanned aerial systems) and digital photogrammetric image processing. Such data currently complement classical remote sensing methods (satellite imagery), providing both improved resolution and high temporal repeatability. Indeed, short acquisition time and flexibility allows measurements within very short time intervals, a requirement when short events are significant in the whole system evolution: The speed at which climatic change‐related events occur requires such fine‐grained spatial and temporal monitoring.This work highlights an increase of sediment transfers during the last decade that ties in with the increasing liquid precipitation as well as a trend of rising temperatures. The newly deglaciated area, particularly at the glacier front, is in constant and fast reshaping, which is quantifiable from 1 year to another, assessing the increase of periglacial landscape modification. This small‐scale detailed analysis enlightens on global processes occurring in Arctic regions demonstrating ongoing geomorphological and landscape changes as a consequence of glacier retreat and newly exposed periglacial environments