POLAR NIGHT Marine Ecology by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030332082
Publisher: Springer International Publishing

6.9 Climate Change Perspectives: Benthos in the New Polar Night

It is clear from recent studies (Berge et al. 2015b, and those reviewed by Berge 2015a and in this volume), that biological processes do not cease during the Polar Night. In benthic systems, this is particularly dramatic, but strong seasonality does exist in many parameters measured in many Arctic locations. For example, we have shown here that seasonality of quality and quantity of food inputs to the benthos contributes strongly to determining community structure and function. Exceptions to this, where strong spatial variation and/or low seasonality exists, however, may suggest new underlying mechanisms and drivers. Many of these insights revolve around alternative sources of food, particularly on continental shelves. We expect ongoing climate change to alter many physical, biological, and chemical drivers of these potential food sources, perhaps altering how we view the benthos during the Polar Night.

Climate warming is affecting the Arctic more significantly than most other areas in the world’s oceans (ACIA 2005). Declining coverage and thickness of sea ice, accelerating retreat of glaciers, increased coastal erosion, and increasing air and sea temperatures are likely to affect strongly Arctic coastal benthos and arguably deep-sea benthic communities as well. As mentioned above, kelp communities are expected to expand northward and into deeper waters due to increasing light, and circumstantial evidence already supports this prediction (Krause-Jensen et al. 2012), although effects of grazers, sedimentation, and warmer temperatures may affect growth and survival of early life stages of kelps (Zacher et al. 2016) and the carbon they provide for the ecosystem. Time-series data have also indicated dramatic increases in cover of other macroalgae in some areas (Kortsch et al. 2012). These developments hint at more macroalgal-based food for benthic systems, enhancing resources for both grazers on the macroalgae, and organisms assimilating detrital carbon. This could improve winter-feeding and settlement conditions for benthic organisms, lessening the seasonal extremes we see in many areas today.

Whereas much of the focus of climate change has been, understandably, on sea ice, change in or decoupling of river/sea-ice phenologies is also likely to have strong impacts on benthic communities and carbon cycling in the coastal Arctic (Macdonald et al. 2015, 2018). Later freeze-up and early ice melt will extend the period of river flow into the Arctic coastal region. Whereas winter (November–April) inputs by the six largest Arctic rivers constitute only 5% of the annual total (McClelland et al. 2016), broadening of seasonality of river flow may substantially increase organic carbon and nitrogen inputs from land. Coupled with permafrost melting and mobilization of modern and ancient carbon and increased coastal erosion, this means greater delivery of terrestrial organic carbon to coastal communities. Due to very little top soil (decomposing terrestrial plants) in some Arctic areas (e.g. Svalbard), however, the expected importance of terrestrial organic carbon is and most likely will remain low for some marine ecosystems. Once thought to be largely inert, recent evidence indicates substantial lability of this material (Bröder et al. 2018) and rapid incorporation into coastal benthic food webs (e.

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