To inform water quality monitoring techniques and modeling at coastal research sites, this study investigated seasonality and trends in coastal lagoons on the eastern shore of Virginia, USA. Seasonality was quantified with harmonic analysis of low-frequency time-series, approximately 30 years of quarterly sampled data at thirteen mainland, lagoon, and ocean inlet sites, along with 4–6 years of high-frequency, 15-min resolution sonde data at two mainland sites. Temperature, dissolved oxygen, and apparent oxygen utilization (AOU) seasonality were dominated by annual harmonics, while salinity and chlorophyll-a exhibited mixed annual and semi-annual harmonics. Mainland sites had larger seasonal amplitudes and higher peak summer values for temperature, chlorophyll-a and AOU, likely from longer water residence times, shallower waters, and proximity to marshes and uplands. Based on the statistical subsampling of high-frequency data, one to several decades of low-frequency data (at quarterly sampling) were needed to quantify the climatological seasonal cycle within specified confidence intervals. Statistically significant decadal warming and increasing chlorophyll-a concentrations were found at a sub-set of mainland sites, with no distinct geographic patterns for other water quality trends. The analysis highlighted challenges in detecting long-term trends in coastal water quality at sites sampled at low frequency with large seasonal and interannual variability.

Stable isotopes are a powerful tool for reconstructing the past. However, environmental factors not previously considered can lead to misinterpretations. Our study presents a novel analysis of the feeding behavior of the megafauna that inhabited the Pilauco ecosystem in south-central Chile during the last glacial termination. We analyzed a suite of modern plant and animal samples from closed-canopy forests to establish an isotopic baseline with which to compare stable isotope results from fossil megafauna. Using the modern samples as a reference, the δ13C results from the Pilauco megafauna indicate feeding behaviors in forested areas. These results were then calibrated with dental calculus samples and coprolites, which suggest the coexistence of graze- and grass-dominated mixed-feeder diets. The δ15N values found in Pilauco megafauna are not consistent with modern reference data sets or with the low δ15N values of extinct proboscideans from other contemporaneous and nearby sites. Probably, the δ15N values of the Pilauco ecosystem were not primarily affected by climate, but rather by disturbance factors (e.g., grazing effect). Our results indicate that the Pilauco megafauna fed mainly on arboreal vegetation; however, non-isotopic proxies indicate that they were also eating open vegetation (e.g., herbs and grasses).

The Subglacial Antarctic Lakes Scientific Access (SALSA) Project accessed Mercer Subglacial Lake using environmentally clean hot-water drilling to examine interactions among ice, water, sediment, rock, microbes and carbon reservoirs within the lake water column and underlying sediments. A ~0.4 m diameter borehole was melted through 1087 m of ice and maintained over ~10 days, allowing observation of ice properties and collection of water and sediment with various tools. Over this period, SALSA collected: 60 L of lake water and 10 L of deep borehole water; microbes >0.2 μm in diameter from in situ filtration of ~100 L of lake water; 10 multicores 0.32–0.49 m long; 1.0 and 1.76 m long gravity cores; three conductivity–temperature–depth profiles of borehole and lake water; five discrete depth current meter measurements in the lake and images of ice, the lake water–ice interface and lake sediments. Temperature and conductivity data showed the hydrodynamic character of water mixing between the borehole and lake after entry. Models simulating melting of the ~6 m thick basal accreted ice layer imply that debris fall-out through the ~15 m water column to the lake sediments from borehole melting had little effect on the stratigraphy of surficial sediment cores.

Distant glacial areas are interconnected by a complex system of fractures and water channels which run in the glacier interior and characterize the englacial realm. Water can slowly freeze in these channels where the slow freezing excludes air bubbles giving the ice a clear aspect. This ice is uplifted to the surface ablation zone by glacial movements and can therefore be observed in the form of clear surface ice bands. We employed an indirect method to sample englacial water by coring these ice bands. We were able, for the first time, to compare microbial communities sampled from clear (i.e. frozen englacial water bands) and cloudy ice (i.e. meteoric ice) through 16S rRNA gene sequencing. Although microbial communities were primarily shaped and structured by their spatial distribution on the glacier, ice type was a clear secondary factor. One area of the glacier, in particular, presented significant microbial community clear/cloudy ice differences. Although the clear ice and supraglacial communities showed typical cold-adapted glacial communities, the cloudy ice had a less defined glacial community and ubiquitous environmental organisms. These results highlight the role of englacial channels in the microbial dispersion within the glacier and, possibly, in the shaping of glacial microbial communities.

The biogeochemical cycling of gold has been proposed from studies focusing on gold particle morphology, surface textures and associated bacteria living on the surface of gold particles. Additionally, it has been suggested that metabolically active bacteria on particles catalyse gold dissolution and gold re-precipitation processes, i.e. fluid–bacterial–mineral interaction within microenvironments surrounding particles. Therefore, the isolation and characterisation of viable bacteria from gold particles can be used as a model to improve the understanding of bacterial–gold interactions. In this study, classical microbiology methods were used to isolate a gold-tolerant bacterium (Acinetobacter sp. SK-43) directly from gold particles. The genome of this isolate contained diverse (laterally acquired) heavy-metal resistance genes and stress tolerance genes, suggesting that gene expression would confer resistance to a wide range of potentially toxic metals that could occur in the surrounding microenvironment. The presence of these genes, along with genes for nutrient cycling under nutrient-limited conditions highlights the genomic capacity of how Acinetobacter sp. SK-43 could survive on gold particles and remain viable. Laboratory experiments demonstrated that this isolate could grow in the presence of soluble gold up to 20 μM (AuCl3) and that >50% of soluble gold was reduced upon exposure. Collectively, these results suggest that Acinetobacter sp. SK-43 (and presumably similar bacteria) could survive the cytotoxic effects of soluble Au from particles undergoing dissolution. This study provides comprehensive insight on the possible bacterial contributions to gold biogeochemical cycling in natural environments.

Sea ice, which forms in polar and nonpolar areas, transmits light to ice-associated (sympagic) algal communities. To noninvasively study the distribution of sea-ice algae, empirical relations to estimate its biomass from under-ice hyperspectral irradiance have been developed in the Arctic and Antarctica but lack for nonpolar regions. This study examines relationships between normalised difference indices (NDI) calculated from hyperspectral transmittance and sympagic algal biomass in the nonpolar Saroma-ko Lagoon. We analysed physico-biogeochemical properties of snow and land-fast sea ice supporting 27 paired bio-optical measurements along three transects covering an area of over 250 m × 250 m in February 2019. Snow depth (0.08 ± 0.01 m) and ice-bottom brine volume fraction (0.21 ± 0.02) showed low (0.06) and high (0.58) correlations with sea-ice core bottom section chlorophyll a (Chl. a), respectively. Spatial analyses unveiled the patch size of sea-ice Chl. a to be ~65 m, which is in the same range reported from previous studies. A selected NDI (669, 596 nm) explained 63% of algal biomass variability. This reflects the bio-optical properties and environmental conditions of the lagoon that favour the wavelength pair in the orange/red part of the spectrum and suggests the necessity of a specific bio-optical relationship for Saroma-ko Lagoon.

This work presents the results of physical and biological investigations at 27 biogeochemical stations of early winter sea ice in the Ross Sea during the 2017 PIPERS cruise. Only two similar cruises occurred in the past, in 1995 and 1998. The year 2017 was a specific year, in that ice growth in the Central Ross Sea was considerably delayed, compared to previous years. These conditions resulted in lower ice thicknesses and Chl-a burdens, as compared to those observed during the previous cruises. It also resulted in a different structure of the sympagic algal community, unusually dominated by Phaeocystis rather than diatoms. Compared to autumn-winter sea ice in the Weddell Sea (AWECS cruise), the 2017 Ross Sea pack ice displayed similar thickness distribution, but much lower snow cover and therefore nearly no flooding conditions. It is shown that contrasted dynamics of autumnal-winter sea-ice growth between the Weddell Sea and the Ross Sea impacted the development of the sympagic community. Mean/median ice Chl-a concentrations were 3–5 times lower at PIPERS, and the community status there appeared to be more mature (decaying?), based on Phaeopigments/Chl-a ratios. These contrasts are discussed in the light of temporal and spatial differences between the two cruises.

We present the analysis of global sympagic primary production (PP) from 300 years of pre-industrial and historical simulations of the E3SMv1.1-BGC model. The model includes a novel, eight-element sea ice biogeochemical component, MPAS-Seaice zbgc, which is resolved in three spatial dimensions and uses a vertical transport scheme based on internal brine dynamics. Modeled ice algal chlorophyll-a concentrations and column-integrated values are broadly consistent with observations, though chl-a profile fractions indicate that upper ice communities of the Southern Ocean are underestimated. Simulations of polar integrated sea ice PP support the lower bound in published estimates for both polar regions with mean Arctic values of 7.5 and 15.5 TgC/a in the Southern Ocean. However, comparisons of the polar climate state with observations, using a maximal bound for ice algal growth rates, suggest that the Arctic lower bound is a significant underestimation driven by biases in ocean surface nitrate, and that correction of these biases supports as much as 60.7 TgC/a of net Arctic PP. Simulated Southern Ocean sympagic PP is predominantly light-limited, and regional patterns, particularly in the coastal high production band, are found to be negatively correlated with snow thickness.

We investigated whether changes in nutrient availability affected N, P, S and polyphenol concentrations in different leaf-development stages of three brevideciduous and three evergreen dominant woody species in a nutrient-limited savanna woodland in Central Brazil. Treatments included eight years of annual fertilization with 100 kg ha−1 of N, P, N plus P and control, each replicated in four randomized 15 × 15-m plots. All species increased S concentrations (minimum 28%) in young and mature leaves in fertilized plots. Dalbergia miscolobium decreased total phenol concentrations with P (−34.3%, −23.7%) and NP fertilization (−28.2%, −17.1%). Blepharocalyx salicifolius increased total phenol (27.6%, 18.8%) and tannin (46.3%; 43.5%) in P fertilized and increased total phenol (33.9%) and tannin (27.8%, 43.5%) in NP fertilized plots. Total phenol concentration decreased with leaf age in Ouratea hexasperma, Styrax ferrugineus and Blepharocalyx salicifolius, which also decreased tannin concentration with leaf age. For all treatments, brevideciduous species had higher N, P, total phenols and tannin concentrations and lower S concentration than evergreens. These differences between phenological groups suggest that tropical ecosystems responses to environmental changes are more complex than anticipated by global vegetation models, with consequences for predictions in ecosystem functions and resilience.

Proglacial environments are ideal for studying the development of soils through the changes of rocks exposed by glacier retreat to weathering and microbial processes. Carbon (C) and nitrogen (N) contents as well as soil pH and soil elemental compositions are thought to be dominant factors structuring the bacterial, archaeal and fungal communities in the early stages of soil ecosystem formation. However, the functional linkages between C and N contents, soil composition and microbial community structures remain poorly understood. Here, we describe a multivariate analysis of geochemical properties and associated microbial community structures between a moraine and a glaciofluvial outwash in the proglacial area of a High Arctic glacier (Longyearbreen, Svalbard). Our results reveal distinct differences in developmental stages and heterogeneity between the moraine and the glaciofluvial outwash. We observed significant relationships between C and N contents, δ13Corg and δ15N isotopic ratios, weathering and microbial abundance and community structures. We suggest that the observed differences in microbial and geochemical parameters between the moraine and the glaciofluvial outwash are primarily a result of geomorphological variations of the proglacial terrain.

Glaciers retreating in response to climate warming are progressively exposing primary mineral substrates to surface conditions. As primary production is constrained by nitrogen (N) availability in these emerging ecosystems, improving our understanding of how N accumulates with soil formation is of critical concern. In this study, we quantified how the distribution and speciation of N, as well as rates of free-living biological N fixation (BNF), change along a 2000-year chronosequence of soil development in a High Arctic glacier forefield. Our results show the soil N pool increases with time since exposure and that the rate at which it accumulates is influenced by soil texture. Further, all N increases were organically bound in soils which had been ice-free for 0–50 years. This is indicative of N limitation and should promote BNF. Using the acetylene reduction assay technique, we demonstrated that microbially mediated inputs of N only occurred in soils which had been ice-free for 0 and 3 years, and that potential rates of BNF declined with increased N availability. Thus, BNF only supports N accumulation in young soils. When considering that glacier forefields are projected to become more expansive, this study has implications for understanding how ice-free ecosystems will become productive over time.

Dissolved organic matter (DOM) in mountain glaciers is an important source of carbon for downstream aquatic systems, and its impact is expected to increase due to the increased melting rate of glaciers. We present a comprehensive study of Laohugou glacier no. 12 (LHG) at the northern edge of the Tibetan Plateau to characterize the DOM composition and sources by analyzing surface fresh snow, granular ice samples, and snow pit samples which covered a whole year cycle of 2014/15. Excitation–emission matrix fluorescence spectroscopy analysis of the DOM with parallel factor analysis (EEM-PARAFAC) identified four components, including a microbially humic-like component (C1), two protein-like components (C2 and C3) and a terrestrial humic-like component (C4). The use of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) showed that DOM from all these samples was dominated by CHO and CHON molecular formulas, mainly corresponding to lipids and aliphatic/proteins compounds, reflecting the presence of significant amounts of microbially derived and/or deposited biogenic DOM. The molecular compositions of DOM showed more CHON compounds in granular ice than in fresh snow, likely suggesting newly formed DOM from microbes during snowmelting.

Understanding the environmental and biogeochemical behaviour of radionuclides is essential for managing our nuclear legacy safely. Remediation efforts and the concept of geological disposal of nuclear waste focus on immobilizing radionuclides within the subsurface. Here we review recent developments in the understanding of solid-phase capture processes of Cs, Sr, Tc, U, Pu and Np. Abiotic interactions between minerals and these radionuclides (including sorption, reductive precipitation and co-precipitation) have been studied in various conditions. Microbially driven processes are much less well characterized, for example the effects of microbial reduction on the structure and reactivity of existing minerals, or their role in the formation of new minerals. Metabolites released by bacteria can play a role in both mineral dissolution and formation, and better understanding their release and role in mineralization has great potential in the development of solid-phase capture processes for radionuclides.

With the aid of a map of the research landscape covered by this review (created using a cluster-analysis tool, a self-organizing map), we highlight the most promising sequestration processes for specific radionuclides. However, radionuclides exhibit highly species-specific behaviour in their interactions with minerals and microorganisms. More research is required to characterize the role mineral surfaces play in bioreductive immobilization of Pu and Np, the reduction products formed, and their relative stability. Further studies should concentrate on more environmentally relevant experiments that include bacteria, minerals and radionuclides.

Previous studies from our laboratory have suggested a role for indigenous metal-reducing bacteria in the reduction of sediment-bound As(V), and have also shown that a stable enrichment culture of Fe(III)-reducing bacteria was able to mobilize arsenic (as As(III)) from sediments collected from West Bengal (Islam et al., 2004). To identify the Fe(III)-reducing bacteria that may play a role in the reduction of As(V) and mobilization of As(III), we made a detailed molecular analysis of this enrichment culture. It was dominated by a close relative of Geothrix fermentans, but the type strain of this organism was unable to conserve energy for growth via the dissimilatory reduction of As(V), or reduce As(V) present in a defined medium containing fumarate as the electron acceptor. Furthermore, when the cells were grown using soluble Fe(III)-citrate as an electron acceptor in the presence of As(V), bacterial Fe(III) reduction resulted in the precipitation of the Fe(II)-bearing mineral vivianite in 2 weeks. This was accompanied by the efficient removal of As from solution. These results demonstrate that Geothrix fermentans, in common with other key Fe(III)-reducing bacteria such as Geobacter sulfurreducens, does not reduce As(V) enzymatically, but can capture arsenic in Fe(II) minerals formed during respiration using Fe(III) as an electron acceptor. Thus, the reduction of arsenic-bearing Fe(III) oxide minerals is not sufficient to mobilize arsenic, but may result in the formation of Fe(II) biominerals that could potentially act as sinks for arsenic in sediments. Additional mechanisms, including dissimilatory As(V) reduction by other specialist anaerobic bacteria, are implicated in the mobilization of arsenic from sediments.

Interest in mineral–microbe interaction has grown enormously over recent decades, providing information in a puzzle-like manner which points towards an ever increasingly intimate relationship between the two; a relationship that can be truly termed co-evolution. Clay minerals play a very central role in this co-evolving system. Some 20 years ago, clay scientists looked at clay mineral–microbe studies as a peripheral interest only. Now, can clay scientists think that they understand the formation of clay minerals throughout geological history if they do not include life in their models? The answer is probably no, but we do not yet know the relative weight of biological and inorganic factors involved in driving clay-mineral formation and transformation. Similarly, microbiologists are missing out important information if they do not investigate the influence and modifications that minerals, particularly clay minerals, have on microbial activity and evolution. This review attempts to describe the several points relating clay minerals and microorganisms that have been discovered so far. The information obtained is still very incomplete and many opportunities exist for clay scientists to help to write the real history of the biosphere.

In temperate latitudes sheep have a seasonal reproductive behaviour, which imposes strong constraints on husbandry in terms of work organization and availability of animal products. During the last 50 years, researchers have focused on understanding the mechanisms driving small ruminants’ reproduction cycles and finding ways to control them. This characteristic is inherited from their wild ancestor. However, the history of its evolution over the 10 millennia that separates present day European sheep from their Near Eastern ancestors’ remains to be written. This perspective echoes archaeologists’ current attempts at reconstructing ancient pastoral societies’ socio-economical organization. Information related to birth seasonality may be retrieved directly from archaeological sheep teeth. The methodology consists of reconstructing the seasonal cycle record in sheep molars, through sequential analysis of the stable oxygen isotope composition (δ18O) of enamel. Because the timing of tooth development is fixed within a species, inter-individual variability in this parameter reflects birth seasonality. A review of the data obtained from 10 European archaeological sites dated from the 6th to the 3rd millennia BC is provided. The results demonstrate a restricted breeding season for sheep: births occurred over a period of 3 to 4 months, from late winter to early summer at latitudes 43°N to 48°N, while a later onset was observed at a higher latitude (59°N). All conclusions concurred with currently held expectations based on present day sheep physiology, which, aside from the historical significance, contributes to the reinforcing of the methodological basis of the approach. Further study in this area will permit regional variability attributable to technical choices, within global schemes, to be fully reported.

Two geochemical techniques from soil mineralogy were used with lake sediment to reconstruct soil development in the catchments of two lakes—one on outwash and the other on till—in the Great Lakes region. A sodium pyrophosphate extraction provides information about leaching of exchangeable and organically complexed cations from terrestrial sources, while an acidified ammonium oxalate extraction removes mineral materials without well-developed crystalline structure that are indicative of podzolization. More evidence of pedogenesis is preserved in sediment of the lake on outwash—likely a result of greater retention of material within the soil profile in the catchment on till. This difference between the records suggests that excessively well-drained (leaky) catchments may provide better records of soil development than those with higher water-holding capacity. Evidence of acidification and podzolization appeared first at the lake on till and 4500 years later at the lake on outwash. Both records reveal a late Holocene intensification of weathering that coincided with a regional climatic change to greater moisture availability. The variability in weathering rates observed presents a more complex picture of weathering than the simple exponential functions often assumed in chronosequence studies. Use of lake sediment records provides better temporal resolution of significant events in soil formation than could be achieved using a chronosequence approach.