In the Anthropocene, in which we now live, climate change is impacting most life on Earth. Microorganisms support the existence of all higher trophic life forms. To understand how humans and other life forms on Earth (including those we are yet to discover) can withstand anthropogenic climate change, it is vital to incorporate knowledge of the microbial 'unseen majority'. We must learn not just how microorganisms affect climate change (including production and consumption of greenhouse gases) but also how they will be affected by climate change and other human activities. This Consensus Statement documents the central role and global importance of microorganisms in climate change biology. It also puts humanity on notice that the impact of climate change will depend heavily on responses of microorganisms, which are essential for achieving an environmentally sustainable future.

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Scientists' Warning to Humanity: Microorganisms and Climate Change

Understanding the dynamics of methane (CH4) emissions is of paramount importance because CH4 has 25 times the global warming potential of carbon dioxide (CO2) and is currently the second most important anthropogenic greenhouse gas. Wetlands are the single largest natural CH4 source with median emissions from published studies of 164 Tg yr 1 , which is about a third of total global emissions. We provide a perspective on important new frontiers in obtaining a better understanding of CH4 dynamics in natural systems, with a focus on wetlands. One of the most exciting recent developments in this field is the attempt to integrate the different methodologies and spatial scales of biogeochemistry, molecular microbiology, and modeling, and thus this is a major focus of this review. Our specific objectives are to provide an up-to-date synthesis of estimates of global CH4 emissions from wetlands and other freshwater aquatic ecosystems, briefly summarize major biogeophysical controls over CH4 emissions from wetlands, suggest new frontiers in CH4 biogeochemistry, examine relationships between methanogen community structure and CH4 dynamics in situ, and to review the current generation of CH4 models. We highlight throughout some of the most pressing issues concerning global change and feedbacks on CH4 emissions from natural ecosystems. Major uncertainties in estimating current and future CH4 emissions from natural ecosystems include the following: (i) A number of important controls over CH4 production, consumption, and transport have not been, or are inadequately, incorporated into existing CH4 biogeochemistry models. (ii) Significant errors in regional and global emission estimates are derived from large spatial-scale extrapolations from highly heterogeneous and often poorly mapped wetland complexes. (iii) The limited number of observations of CH4 fluxes and their associated environmental variables loosely constrains the parameterization of process-based biogeochemistry models.

/pdf/methane-emissions-from-wetlands-biogeochemical-microbial-and-4fsuddj4v7.pdf

Methane emissions from wetlands: biogeochemical, microbial, and modeling perspectives from local to global scales

Microplastics (MP) are recognized as a growing environmental hazard and have been identified as far as the remote Polar Regions, with particularly high concentrations of microplastics in sea ice. Little is known regarding the horizontal variability of MP within sea ice and how the underlying water body affects MP composition during sea ice growth. Here we show that sea ice MP has no uniform polymer composition and that, depending on the growth region and drift paths of the sea ice, unique MP patterns can be observed in different sea ice horizons. Thus even in remote regions such as the Arctic Ocean, certain MP indicate the presence of localized sources. Increasing exploitation of Arctic resources will likely lead to a higher MP load in the Arctic sea ice and will enhance the release of MP in the areas of strong seasonal sea ice melt and the outflow gateways.

/pdf/arctic-sea-ice-is-an-important-temporal-sink-and-means-of-1fbvqr64d4.pdf

Arctic sea ice is an important temporal sink and means of transport for microplastic

Although mounting evidence suggests the ubiquity of microplastic in aquatic ecosystems worldwide, our knowledge of its distribution in remote environments such as Polar Regions and the deep sea is scarce. Here, we analyzed nine sediment samples taken at the HAUSGARTEN observatory in the Arctic at 2340–5570 m depth. Density separation by MicroPlastic Sediment Separator and treatment with Fenton’s reagent enabled analysis via Attenuated Total Reflection FTIR and μFTIR spectroscopy. Our analyses indicate the wide spread of high numbers of microplastics (42–6595 microplastics kg–1). The northernmost stations harbored the highest quantities, indicating sea ice as a possible transport vehicle. A positive correlation between microplastic abundance and chlorophyll a content suggests vertical export via incorporation in sinking (ice-) algal aggregates. Overall, 18 different polymers were detected. Chlorinated polyethylene accounted for the largest proportion (38%), followed by polyamide (22%) and polypropylene (16...

High Quantities of Microplastic in Arctic Deep-Sea Sediments from the HAUSGARTEN Observatory.

BACKGROUND Marine ecosystems are composed of a diverse array of life forms, the majority of which are unicellular—archaea, bacteria, and eukaryotes. The power of these microbes to process carbon, shape Earth’s atmosphere, and fuel marine food webs has been established over the past 40 years. The marine biosphere is responsible for approximately half of global primary production, rivaling that of land plants. Unicellular eukaryotes (protists) are major contributors to this ocean productivity. In addition to photosynthetic growth, protists exhibit a range of other trophic modes, including predation, mixotrophy (a combination of photosynthetic and predatory-based nutrition), parasitism, symbiosis, osmotrophy, and saprotrophy (wherein extracellular enzymes break down organic matter to smaller compounds that are then transported into the cell by osmotrophy). ADVANCES Sensitive field approaches have illuminated the enormous diversity of protistan life (much of it uncultured) and, coupled with activity measurements, are leading to hypotheses about their ecological roles. In parallel, large-scale sequencing projects are providing fundamental advances in knowledge of genome/gene composition, especially among photosynthetic lineages, many of which are complex amalgams derived from multiple endosymbiotic mergers. Marine protists have yielded insight into basic biology, evolution, and molecular machineries that control organismal responses to the environment. These studies reveal tightly controlled signaling and transcriptional regulation as well as responses to limitation of resources such as iron, nitrogen, and vitamins, and offer understanding of animal and plant evolution. With the formulation of better computational approaches, hypotheses about interactions and trophic exchanges are becoming more exact and modelers more assertive at integrating different data types. At the same time, the impacts of climate change are being reported in multiple systems, of which polar environments are the touchstone of change. OUTLOOK Driven by the need to translate the biology of cells into processes at global scales, researchers must bring the conceptual framework of systems biology into bigger “ecosystems biology” models that broadly capture the geochemical activities of interacting plankton networks. Existing data show that protists are major components of marine food webs, but deducing and quantifying their ecosystem linkages and the resulting influences on carbon cycling is difficult. Genome-based functional predictions are complicated by the importance of cellular structures and flexible behaviors in protists, which are inherently more difficult to infer than the biochemical pathways typically studied in prokaryotes. Alongside the plethora of genes of unknown function, manipulable genetic systems are rare for marine protists. The development of genetic systems and gene editing for diverse, ecologically important lineages, as well as innovative tools for preserving microbe-microbe interactions during sampling, for visual observation, and for quantifying biogeochemical transformations, are critical but attainable goals. These must be implemented in both field work and laboratory physiology studies that examine multiple environmental factors. Expanding genome functional predictions to identify the molecular underpinnings of protistan trophic modes and realistically constrain metabolism will position the field to build reliable cell systems biology models and link these to field studies. By factoring in true complexities, we can capture key elements of protistan interactions for assimilation into more predictive global carbon cycle models.

http://science.sciencemag.org/content/sci/347/6223/1257594.full.pdf

Rethinking the marine carbon cycle: Factoring in the multifarious lifestyles of microbes

In the Arctic, under-ice primary production is limited to summer months and is restricted not only by ice thickness and snow cover but also by the stratification of the water column, which constrains nutrient supply for algal growth. Research Vessel Polarstern visited the ice-covered eastern-central basins between 82° to 89°N and 30° to 130°E in summer 2012, when Arctic sea ice declined to a record minimum. During this cruise, we observed a widespread deposition of ice algal biomass of on average 9 grams of carbon per square meter to the deep-sea floor of the central Arctic basins. Data from this cruise will contribute to assessing the effect of current climate change on Arctic productivity, biodiversity, and ecological function.

http://science.sciencemag.org/content/sci/339/6126/1430.full.pdf

Export of Algal Biomass from the Melting Arctic Sea Ice

. A methane surplus relative to the atmospheric equilibrium is a frequently observed feature of ocean surface water. Despite the common fact that biological processes are responsible for its origin, the formation of methane in aerobic surface water is still poorly understood. We report on methane production in the central Arctic Ocean, which was exclusively detected in Pacific derived water but not nearby in Atlantic derived water. The two water masses are distinguished by their different nitrate to phosphate ratios. We show that methane production occurs if nitrate is depleted but phosphate is available as a P source. Apparently the low N:P ratio enhances the ability of bacteria to compete for phosphate while the phytoplankton metabolite dimethylsulfoniopropionate (DMSP) is utilized as a C source. This was verified by experimentally induced methane production in DMSP spiked Arctic sea water. Accordingly we propose that methylated compounds may serve as precursors for methane and thermodynamic calculations show that methylotrophic methanogenesis can provide energy in aerobic environments.

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Methane production in aerobic oligotrophic surface water in the central Arctic Ocean

. The ice-covered central Arctic Ocean is characterized by low primary productivity due to light and nutrient limitations. The recent reduction in ice cover has the potential to substantially increase phytoplankton primary production, but little is yet known about the fate of the ice-associated primary production and of the nutrient supply with increasing warming. This study presents results from the central Arctic Ocean collected during summer 2012, when sea-ice extent reached its lowest ever recorded since the onset of satellite observations. Net primary productivity (NPP) was measured in the water column, sea ice and melt ponds by 14CO2 uptake at different irradiances. Photosynthesis vs. irradiance (PI) curves were established in laboratory experiments and used to upscale measured NPP to the deep Eurasian Basin (north of 78° N) using the irradiance-based Central Arctic Ocean Primary Productivity (CAOPP) model. In addition, new annual production has been calculated from the seasonal nutrient drawdown in the mixed layer since last winter. Results show that ice algae can contribute up to 60% to primary production in the central Arctic Ocean at the end of the productive season (August–September). The ice-covered water column has lower NPP rates than open water due to light limitation in late summer. As indicated by the nutrient ratios in the euphotic zone, nitrate was limiting primary production in the deep Eurasian Basin close to the Laptev Sea area, while silicate was the main limiting nutrient at the ice margin near the Atlantic inflow. Although sea-ice cover was substantially reduced in 2012, total annual new production in the Eurasian Basin was 17 ± 7 Tg C yr−1, which is within the range of estimates of previous years. However, when adding the contribution by sub-ice algae, the annual production for the deep Eurasian Basin (north of 78° N) could double previous estimates for that area with a surplus of 16 Tg C yr−1. Our data suggest that sub-ice algae are an important component of the productivity in the ice-covered Eurasian Basin of the central Arctic Ocean. It remains an important question whether their contribution to productivity is on the rise with thinning ice, or whether it will decline due to overall sea-ice retreat and be replaced by phytoplankton.

/pdf/photosynthetic-production-in-the-central-arctic-ocean-during-443kt17afv.pdf

Karel Bakker

Papers

Export of Algal Biomass from the Melting Arctic Sea Ice

Methane production in aerobic oligotrophic surface water in the central Arctic Ocean

Photosynthetic production in the central Arctic Ocean during the record sea-ice minimum in 2012

Impacts of sea-ice retreat on primary production in the Central Arctic Ocean