Rivers and groundwater are major sources of nutrients to the global coastal ocean. Climate change is expected to impact nutrient fluxes from river basins and coastal aquifers through alterations to both hydrological and nutrient cycling processes. In this Review, we identify and summarize how climate change impacts, such as changes in precipitation, increased cryosphere melt, and sea level rise, will affect water discharge and nutrient concentrations in rivers and coastal groundwater, which ultimately control nutrient inputs to the coastal ocean. We also document key limitations in the current understanding of climate-related changes to nutrient fluxes, especially in coastal groundwater basins. The impacts of climate change will interact with local human impacts, highlighting the need for studies spanning local to global scales to better understand and improve predictions of future nutrient fluxes from these hydrological pathways. Nutrient fluxes from rivers and groundwater flowing into the ocean are impacted by climate change impacts such as precipitation changes, cryosphere melt, and sea level rise.

We investigated the effect of decreased pH on the morphology and nutrient physiology of the cosmopolitan marine diatom Thalassiosira rotula (CCMP3362) by acclimating unialgal cultures to two different CO2 gas concentrations under optimal light, temperature and nutrient conditions. At lower pH (higher CO2), T. rotula exhibited a reduction in cell diameter (7%), surface area (13%), and volume (20%), and an increase in surface area-to-volume ratio (7%). All measures of silicification in T. rotula, i.e., silica (SiO2) quota, rate of silicic acid (Si(OH)(4)) utilization, and elemental ratios of SiO2:C and SiO2:N, remained unchanged. Similarly, carbon (C) and nitrogen (N) quotas, ratios and utilization rates were mostly unaffected by pH. In contrast, the utilization rate of nitrate (rho NO3) was significantly lower at decreased pH when the rate was normalized by cell number instead of by cell volume. The changes in cell morphology found in this study under low pH were likely not large enough to significantly impact physiological processes and the role of this species in marine food webs and biogeochemical cycles. It is possible that the interactive effects of pH, temperature, light, and nutrient availability characteristic of different regions of the world ocean could result in stronger physiological and morphological responses in this widespread diatom. However, under constant optimal growth conditions, T. rotula was only mildly affected by changes in pH, and in particular the physiology and elemental stoichiometry of C, N and Si were not sensitive to acidification.

Phytoplankton are the base of nearly all marine food webs and mediate the interactions of biotic and abiotic components in marine systems. Understanding the spatial and temporal changes in phytoplankton growth requires comprehensive biological, physical, and chemical information. Long-term datasets are an invaluable tool to study these changes, but they are rare and often include only a small set of measurements. Here, we present biological, physical and chemical oceanographic data measured periodically between March 2010 and November 2017 from the euphotic zone of Saanich Inlet, a temperate fjord on the west coast of British Columbia, Canada. The dataset includes measurements of dissolved macronutrients, total and size-fractionated chlorophyll-a, particulate carbon, nitrogen and biogenic silica, and carbon and nitrate uptake rates. This collection describes phytoplankton dynamics and the distribution of biologically-available macronutrients over time in the upper water column of Saanich Inlet. We establish a baseline for future investigations in Saanich Inlet and provide a data collection protocol that can be applied to similar productive coastal regions.

We present measurements of the silicon isotopic composition of silicic acid (δ 30 Si‐Si(OH) 4 ) from seawater collected along a transect following one of the main flow paths of Pacific‐origin waters through the Arctic Ocean during the Canadian Arctic GEOTRACES and Distributed Biological Observatory expeditions in the summer of 2015. The δ 30 Si‐Si(OH) 4 signals track the modification of Pacific‐origin waters as they transit from west to east, and reflect the distribution of water masses, the dissolution of biogenic silica (bSiO 2 ), and the biological utilization of Si in surface waters. Pacific‐origin waters have lower δ 30 Si‐Si(OH) 4 values than the surrounding water masses and are closely linked with a tongue of nutrient‐rich cold water that can be traced back to the Bering Strait. The δ 30 Si‐Si(OH) 4 measurements indicate that the high [Si(OH) 4 ] in the deep waters of Baffin Bay are driven entirely by dissolution of exported bSiO 2 . Using an open‐system model, we estimate the biogenic Si isotope effect ( 30 ε) for the Bering and Chukchi Seas, and the Canadian Arctic Archipelago to be 30 ε = −1.18 ± 0.02‰ (1SE), which agrees very well with laboratory and field estimates. In contrast, the isotope systematics in the Canada Basin and Baffin Bay are better represented by a closed‐system model. We also present an approach to estimate production by sea‐ice algae using δ 30 Si‐Si(OH) 4 signals, though a better understanding of the sea‐ice/water column Si systematics in the Arctic is needed to confirm the viability of this approach.

The NASA EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) program was established to better quantify the pathways of the biological carbon pump in order to gain a more comprehensive understanding of global carbon export efficiency. The summer 2018 field campaign in the vicinity of Ocean Station Papa (Station P; 50°N, 145°W) in the Northeast Pacific Ocean yielded evidence of low phytoplankton biomass and primary productivity dominated by small cells (<5 µm) that are reliant on recycled nutrients. Using combined 13C/15N stable isotope incubations, we calculated an average depth-integrated dissolved inorganic carbon uptake (net primary production) rate of 23.1 mmol C m–2 d–1 throughout the euphotic zone with small cells contributing 88.9% of the total daily DIC uptake. Average depth-integrated NO3– uptake rates were 1.5 mmol N m–2 d–1 with small cells contributing 73.4% of the total daily NO3– uptake. Estimates of new and regenerated production fluctuated, with small cells continuing to dominate both forms of production. The daily mixed-layer f-ratio ranged from 0.17 to 0.38 for the whole community, consistent with previous studies, which indicates a predominance of regenerated production in this region, with small and large cells (≥5 μm) having average f-ratios of 0.28 and 0.82, respectively. Peak phytoplankton biomass, total primary productivity and new production occurred between Julian Days 238 and 242 of our observation period, driven primarily by an increase in carbon and nitrate assimilation rates without apparent substantial shifts in the phytoplankton size-class structure. Our findings demonstrate the importance of small cells in performing the majority of net primary production and new production and the modest productivity fluctuations that occur in this iron-limited region of the Northeast Pacific Ocean, driven by ephemeral increases in new production, which could have significant ramifications for carbon export over broad timescales.

Diatoms are major contributors to marine primary productivity and carbon export due to their rapid growth in high-nutrient environments and their heavy silica ballast. Their contributions are highly modified in high-nutrient low-chlorophyll regions due to the decoupling of upper-ocean silicon and carbon cycling caused by low iron (Fe). The Si cycle and the role of diatoms in the biological carbon pump was examined at Ocean Station Papa (OSP) in the HNLC region of the northeastern subarctic Pacific during the NASA EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field study. Sampling occurred during the annual minimum in surface silicic acid (Si(OH)4) concentration. Biogenic silica (bSi) concentrations were low, being in the tens of nanomolar range, despite high Si(OH)4 concentrations of about 15 μM. On average, the >5.0-µm particle size fraction dominated Si dynamics, accounting for 65% of bSi stocks and 81% of Si uptake compared to the small fraction (0.6–5.0 μm). Limitation of Si uptake was detected in the small, but not the large, size fraction. Growth rate in small diatoms was limited by Fe, while their Si uptake was restricted by Si(OH)4 concentration, whereas larger diatoms were only growth-limited by Fe. About a third of bSi production was exported out of the upper 100 m. The contribution of diatoms to carbon export (9–13%) was about twice their contribution to primary productivity (3–7%). The combination of low bSi production, low diatom primary productivity and high bSi export efficiency at OSP was more similar to the dynamics in the subtropical gyres than to other high-nutrient low-chlorophyll regions.

Marine phytoplankton can utilize different strategies to cope with ocean warming and freshening from glacial melting in polar regions, which are disproportionally impacted by global warming. In the present study, we investigated the individual and combined effects of a 4 °C increase in seawater temperature (T+) and a 4 psu decrease in salinity (S−) from ambient values on biomass, nutrient use, fatty acid composition and lipid damage biochemistry of natural phytoplankton assemblages from Potter Cove (25 de Mayo/King George Island, Antarctica). Experiments were conducted by exposing the assemblages to four treatments during a 7-day incubation period using microcosm located along shore from January 23 to 31, 2016. The N:P ratio decreased in all treatments from day 4 onwards, but especially under high temperature (T+). Lipid damage was mainly detected under S0T+ and S−T+ conditions, and it decreased when the production of the antioxidant α-tocopherol increased. This antioxidant protection resulted in a build-up of phytoplankton biomass, especially at T+. Under the combined effect of both stressors (S−T+), the concentration of ω3 fatty acids increased, potentially leading to higher-quality FA composition. These results, which were related to the dominance of sub-Antarctic species in phytoplankton assemblages, contribute to the understanding of the potential consequences of ocean warming and increase seawater freshening on the trophic webs of the Southern Ocean.

Resistance to algae contamination is an important characteristic of insulators used in overhead power distribution in coastal environments. It is therefore important to understand the parameters governing algae adhesion onto polymer insulator materials such as silicone. Flow cell-based shear experiments were conducted in order to characterize the adhesion strength of algae onto polydimethylsiloxane surfaces, comparing fresh polymer substrates with those that have been soaked in water and saline solutions for 1 month. Both freshwater algae and seawater species could withstand considerably less drag force and were therefore more easily removed when the polymer was soaked in salt water. The polymer surface was found to be unaltered in terms of its roughness, contact angle, and lack of water uptake; no macroscopic surface characterization was therefore able to account for the differences in cell adhesion strength resulting from the soaking treatment. Surface-specific nonlinear vibrational spectroscopy, however, revealed subtle differences in the orientation of surface methyl groups that resulted from the water and saline exposure.

Details of the design and implementation of an open-source platform for studying the adhesion of cells attached to solid substrata are provided. The hardware is based on a laser-cut flow channel connected to a programmable syringe pump. The software automates all aspects of the flow rate profile, data acquisition and image analysis. An example of the pelagic diatom Thalassiosira rotula adhered to poly(dimethyl siloxane) surfaces is provided. The procedure described enables the shear rate to be converted to drag force for arbitrary shaped objects, of utility to the study of many cell species, especially ones that are obviously non-spherical. It was determined that 90% of cells are removed with the application of drag forces < 3 x 10(12) N, and that this value is relatively independent of the incubation time on the surface. This result is important to understand how marine species interact with polymer surfaces that are used in electrical insulator applications.

The climate around the Western Antarctic Peninsula (WAP) is rapidly changing and dramatically affecting marine coastal waters. Increases in air and seawater temperatures, not matter how small, can alter coastal biological communities due to both temperature increases as well as salinity reduction from glacier melting. The aim of this study was to evaluate the individual and combined effects of elevated sea surface temperature (+ 4 degrees C) and decreased salinity (-4) on growth and assemblage composition of natural summer phytoplankton from Potter Cove (King George Island, South Shetlands, northern WAP), using an outdoor microcosm experiment. Pigment composition was analyzed by high performance liquid chromatography (HPLC/Chemtax) and species composition by light and electron microscopy. Increases in phytoplankton biomass during the first 3 days at elevated-temperatures coincided with an increase in the abundance and the specific growth rate of small centric diatoms (Chaetoceros socialis and Shionodiscus gaarderae, mostly observed in temperate waters) and unidentified small phytoflagellates < 5 mu m. In contrast, pennate diatoms significantly decreased. At the end of the experiment on day 7, under nitrate and phosphate limitation, chlorophytes abundances increased under low salinity whereas prasinophytes decreased in all treatments. This study suggests that climate change could notably affect Antarctic phytoplankton composition by favouring temperate-water species previously undetected in Antarctic waters, such us S. gaarderae. Moreover, the observed changes in phytoplankton structure, associated with an increase of nano- over micro-size taxa, could have important implications for future Antarctic food webs.

We present a decade of dissolved and particulate silica concentrations within five biological “hot spots” in the Pacific Arctic Region (PAR) and the first measurements of both biogenic silica production rates (ρSi) and the kinetics of silicon utilization from a period of four years at the same sites. The “hot spots” were located within the Bering and Chukchi Seas and identified as part of the Distributed Biological Observatory (DBO). Across all hot spots, the highest concentrations of silicic acid (Si(OH)4) and biogenic silica were found near the bottom of the euphotic zone and often correlated with increased ρSi. For the entire region, the average ρSi was 19 mmol m−2 day−1 and siliceous microplankton (i.e., diatoms) contributed an average of 62% to primary productivity and 82% to nitrate utilization. Irradiance and [Si(OH)4] had separate and interactive effects on ρSi. Irradiance modulated both the magnitude of ρSi and the response of diatoms to changes in Si(OH)4. Availability of Si(OH)4 limited ρSi in all hot spots in at least one of the four years. Kinetic experiments conducted in all hot spots demonstrated that the half‐saturation constant (Ks) for ρSi was 4–8 times higher than ever reported in the literature. In the southeastern Chukchi Sea, an east to west gradient in [bSiO2] and ρSi may have been driven by differences in the availability of NO3− rather than Si(OH)4. Despite strong interannual variability, we suggest that phytoplankton phenology responds to short‐term climatic changes, which can have far‐reaching effects on Arctic regions influenced by the Pacific‐origin waters flowing through the PAR.

Coastal phytoplankton assemblages from Potter Cove in Antarctica were exposed to low salinity (S-) and high temperature (T +) conditions to simulate oceanic changes resulting from global warming. The treatments were: low salinity (30) and high temperature (S-T +); low salinity and ambient temperature (1-2 degrees C) (S-T0); ambient salinity (34) and increased temperature (4-5 degrees C) (SOT +) and ambient salinity with ambient temperature (control, SOTO). Experiments were conducted in 100-L microcosms and monitored for 6 days. Compared to the control treatment, micro-size diatoms (25-50 mu m) dominated the phytoplankton assemblages while prasinophyceae were less abundant at the end of the S-T +/- and SOT + treatments. Nano-size diatoms (10-20 mu m) also increased significantly at the end of the experiment but only when exposed to SOT +. In S- treatments, the production of reactive oxygen/ nitrogen species (ROS/RNS) increased while phytoplankton biomass decreased. Under T+ conditions, the production of ROS/RNS was significantly lower than in T0 treatments. Throughout the experiment, alpha-Tocopherol (alpha-T) consumption may have prevented lipid damage, allowing for increases in photosynthetic rate and growth when nutrients concentrations were sufficiently high. Our results indicate that an increase in temperature can compensate for the lipid damage produced by low salinity, and stimulate carbon uptake in both conditions. This study demonstrated that the final composition of phytoplankton assemblages in all experimental treatments was strongly influenced by the original composition. Future changes in natural phytoplankton assemblages in Antarctic coastal waters will therefore depend on the planktonic species present at the time of the perturbation, which can strongly impact energy flow along food webs and the magnitude of carbon and nutrient fluxes in Antarctic waters.

For photosynthetic microbial eukaryotes, the rate-limiting step in NO3- assimilation is its reduction to nitrite (NO2-), which is catalyzed by assimilatory nitrate reductase (NR). Oceanic productivity is primarily limited by available nitrogen and, although nitrate is the most abundant form of available nitrogen in oceanic waters, little is known about the identity of microbial eukaryotes that take up nitrate. This lack of knowledge is especially severe for ice-covered seas that are being profoundly affected by climate change. To address this, we examined the distribution and diversity of NR genes in the Arctic region by way of clone libraries and data mining of available metagenomes (total of 4.24 billion reads). We directly compared NR clone phylogenies with the V4 region of the 18S rRNA gene (DNA pool) and 18S rRNA (RNA pool) at two ice-influenced stations in the Canada Basin (Beaufort Sea). The communities from the two nucleic acid templates were similar at the level of major groups, and species identified by way of NR gene phylogeny and microscopy were a subset of the 18S results. Most NR genes from arctic clone libraries matched diatoms and chromist nanoflagellates, including novel clades, while the NR genes in arctic eukaryote metagenomes were dominated by chlorophyte NR, in keeping with the ubiquitous occurrence of Mamiellophyceae in the Arctic Ocean. Overall, these data suggest that a dynamic and mixed eukaryotic community utilizes nitrate across the Arctic region, and they show the potential utility of NR as a tool to identify ongoing changes in arctic photosynthetic communities.IMPORTANCE To better understand the diversity of primary producers in the Arctic Ocean, we targeted a nitrogen cycle gene, NR, which is required for phytoplankton to assimilate nitrate into organic forms of nitrogen macromolecules. We compared this to the more detailed taxonomy from ice-influenced stations using a general taxonomic gene (18S rRNA). NR genes were ubiquitous and could be classified as belonging to diatoms, dinoflagellates, other flagellates, chlorophytes, and unknown microbial eukaryotes, suggesting novel diversity of both species and metabolism in arctic phytoplankton.

We present phytoplankton and nutrient observations from a period of ten years within five biological 'hotspots' in the Bering and Chukchi Seas, as identified by the Distributed Biological Observatory (DBO). Nitrate (NO3-) and total and size-fractionated (< and >5 µm) chlorophyll a (Chl a) concentrations, and rates of carbon (ρC, 'primary productivity') and NO3- utilization (ρNO3) were measured throughout the euphotic zone during eight cruises in July 2006, 2008 and yearly from 2011 to 2016. Samples were collected at one station within each of these five hotspots, which were located south of St. Lawrence Island (DBO1), south of the Bering Strait in the Chirikov Basin (DBO2), in the southeastern (DBO3) and northeastern (DBO4) Chukchi Sea, and in Barrow Canyon (DBO5). Nitrate concentrations averaged over the 10 years increased with depth and euphotic-zone integrated values were highest in the Chirikov Basin. Subsurface maxima in Chl a were present at about 30 m depth at most locations during every cruise, although the maximum ρC and ρNO3 rates were shallower, within the top 10 m of the water column. The f-ratio (calculated as ρNO3/ρC) averaged for all DBO regions and for the 10-year study-period was 0.41 (± 0.24). Similarly, phytoplankton > 5 µm in size accounted for 65 (± 23) % of total Chl a for all regions over the 10 years. Taxonomic analysis done in 2013 showed that diatoms were the dominant taxa throughout all of the DBO regions, with the exception of areas influenced by low-nutrient waters on the eastern side of the Chukchi shelf near the Alaska coast. These coastal waters were dominated by coccolithophores and small (< 7 μm) flagellates and had much lower Chl a concentrations, ρC and ρNO3 than farther west. In addition, the proportion of pennate diatoms to total diatom abundance was found to be elevated relative to centric diatoms when sea-ice was present. Our measurements of phytoplankton biomass and ρC indicated that the higher abundance of pennate diatoms in the euphotic zone was the result of phytoplankton blooms happening below the ice, rather than pennate diatoms being supplied by a sea-ice diatom bloom. The dynamic nature of the Pacific Arctic Region (PAR) resulted in strong interannual variability within each DBO region for all parameters, with no clear increasing or decreasing trends from 2006 to 2016. Spatial variations were more consistent, with the highest rates of ρC and ρNO3 occurring in the nutrient-rich waters of the southeastern Chukchi Sea (away from shore), and decreasing in regions further north as NO3- concentrations were lower. An east-west gradient in phytoplankton biomass and productivity was also observed in the southeastern Chukchi Sea, which can be attributed to differences in the nutrient content of the water masses along the gradient. This study shows that the observed strong interannual variability in phytoplankton biomass and productivity cannot be attributed to differences in methodology or sampling time. It also highlights the need for better temporal and spatial sampling resolution such that the long-term effects of climate-induced changes can be identified against the backdrop of the naturally-strong interannual variability in the PAR.

Marine oxygen minimum zones (OMZs) support 30-50% of global fixed-nitrogen (N) loss but comprise only 7% of total ocean volume. This N-loss is driven by canonical denitrification and anaerobic ammonium oxidation (anammox), and the distribution and activity of these two processes vary greatly in space and time. Factors that regulate N-loss processes are complex, including organic matter availability, oxygen concentrations, and NO2- and NH4+ concentrations. While both denitrification and anammox produce N2, the overall geochemical outcome of these processes are different, as incomplete denitrification, for example, produces N2O, which is a potent greenhouse gas. Rates of anammox and denitrification and more detailed ecophysiological knowledge of the microorganisms catalyzing these processes are needed to develop more robust models of N-loss in OMZs. To this end, we conducted monthly incubations with 15N-labeled N during anoxic conditions and deep-water renewal cycle in Saanich Inlet, British Columbia, a persistently anoxic fjord. Both denitrification and anammox operated throughout the low oxygen water column with depth integrated rates of anammox and denitrification ranging from 0.150.03 to 3.40.3 and 0.020.006 to 142 mmol N2 m-2 d-1, respectively. Most N2 production in Saanich Inlet was driven by denitrification, with high rates developing in response to enhanced substrate supply from deep water renewal. Dynamics in rates of denitrification were linked to shifts in microbial community composition. Notably, periods of intense denitrification were accompanied by blooms in an Arcobacter population against a background community dominated by SUP05 and Marinimicrobia. Rates of N2 production through denitrification and anammox, and their dynamics, were then explored through flux-balance modeling with higher rates of denitrification linked to the physiology of substrate uptake. Overall, both denitrification and anammox operated throughout the year, contributing to an annual N-loss of 2 x 10-3 Tg N2 yr-1, 37% of which we attribute to anammox and 63% to complete denitrification. Extrapolating these rates from Saanich Inlet to all similar coastal inlets in BC (2478 km2), we estimate that these inlets contribute 0.1 % to global pelagic N-loss.

In the summers of 2007 and 2008, we studied assemblages of nano-and microphytoplankton from the subsurface chlorophyll maximum (SCM) across five broad oceanographic domains in the seas surrounding northern North America. These domains are the eastern Subarctic North Pacific (ESNP), Bering and Chukchi Seas (BE-CH), Beaufort Sea and Canada Basin (BS-CB), Canadian Arctic Archipelago (CAA), and Baffin Bay and Labrador Sea (BB-LS). Average abundance and total carbon biomass (C) of phytoplankton (> 2 mu m) varied 10-fold and -20-fold, respectively, across the five domains. In the BE-CH, CAA and BB-LS, diatoms averaged 35-70% and dinoflagellates 11-45% of total phytoplankton C (> 2 pm), whereas in the ESNP and BS-CB, unidentified flagellates/coccoids (2-8 mu m) represented a greater proportion of total C (27% and 39% respectively) than in the other domains. In the BE-CH and BB-LS, phytoplankton C (> 2 gm) was dominated by dinoflagellates of the genus Gymnodinium, centric diatoms including Thalassiosira spp. and Chaetoceros spp., unidentified flagellates/coccoids (2-8 gm), and cryptomonads. In contrast, diatoms such as Thalassiosira spp. and its resting spores dominated C in the CAA, with dinoflagellates being less significant than in the BE-CH and BB-LS. Unidentified flagellates/coccolds (2-8 pm), Gymnodinium spp., and cryptomonads dominated in the ESNP, and particularly in the BS-CB, where diatoms contributed only 18% of the very low levels of total phytoplankton C (> 2 mu m). Phytoplankton C (> 2 mu m) to chlorophyll a ratios (phyto C:chl a) averaged only 31 g C g chl alpha(-1) in the oligotrophic BS-CB domain, and 51-150 g C g chl alpha(-1) in the other domains, whereas ratios of biogenic silica to phytoplankton C (> 2 mu m) (bSi:phyto C) were lowest in the eastern domains. Estimates of phytoplankton C were highly sensitive to the choice of C to cell volume equations (C:vol) adopted in the calculations, particularly in diatom-rich areas. This study highlights how diatoms and dinoflagellates are the main drivers of large-scale variations in C biomass for phytoplankton (> 2 mu m), whereas unidentified flagellates/coccoids (2-8 mu m) make a significant contribution to C biomass in oligotrophic domains, such as BS-CB, where diatoms and dinoflagellates are less abundant. Reduced surface water density (sigma(T)) was associated with deeper SCM layers, and with decreased C biomass of unidentified flagellates/coccoids (2-8 mu m). These observations confirm recent studies highlighting the role of surface water stratification caused by melting sea ice in shaping nano-and microphytoplankton assemblages.

La Peninsula Antartica (PA) es una de las regiones mas afectadas por el calentamiento global, lo cual promueve el derretimiento glaciario y, en consecuencia, una disminucion de la salinidad por incremento de agua dulce al medio marino costero. En este estudio se analizo la respuesta de la comunidad fitoplanctonica de Caleta Potter (Isla 25 de Mayo, Shetlands del Sur, al norte de la PA) al aumento de 4°C de temperatura (T+S0), disminucion de la salinidad de 34 a 30 (T0S-), y la combinacion de ambas variables (T+S-), con respecto al control (T0S0) durante 8 dias de experimento en microcosmos. Se analizo la biomasa y composicion especifica mediante analisis de pigmentos (HPLC), recuentos celulares y observaciones con microscopiaelectronica. Los maximos de biomasa (Cl-a) y densidad celular se observaron el dia 3 (23-28 µgL-1 y 8-9,5x106 celulasL-1) en T+S- y T+S0, y el dia 5 (17-18 µgL-1 y 5-7x106 celulasL-1) en T0S0 y T0S-. La comunidad estuvo ampliamente dominada por diatomeas a lo largo del experimento y en todos los tratamientos. Las diatomeas estuvieron principalmente representadas por organismos nanoplanctonicos (<20µm) del genero Chaetoceros, los cuales incrementaron significativamente su abundancia relativa hacia el final del experimento en T+Sy T+S0. Por otro lado, se observo un aumento significativo de flagelados <5µm (cloroficeas) en T0S- durante el dia 7. Finalmente, las diatomeas pennadas, los dinoflagelados y las prasinoficeas disminuyeron significativamente hacia el dia 7 en todos los tratamientos con respecto al control. Los cambios en la composicion especifica observados en este estudio difieren respecto a trabajos previos, posiblemente debido a diferencias en las abundancias relativas al inicio del experimento. No obstante, en todos ellos en terminos generales se observa una mayor tolerancia de la fraccion nanoplanctonica ante cambios en la temperatura y salinidad.

This paper provides a synthesis of available in situ primary production (PP) measurements from the Pacific Arctic Region (PAR), collected between 1950 and 2012. Seasonal integrated primary production (IPP) across the PAR was calculated from 524 profiles, 340 of which were also analyzed to determine the average vertical distribution of PP rates for spring, summer and fall months. The Chirikov Basin and Chukchi Shelf were the most productive areas, with the East Siberian Sea, Chukchi Plateau and Canada Basin the lowest. Decadal-scale changes were indicated in the southern Chukchi Sea, and across Hanna Shoal. In the southern Chukchi Sea in August, IPP increased significantly from 113±35 mg C m-2 d-1 in 1959 and 1960 to 833±307 mg C m-2 d-1 in the 2000 s. Increases in the magnitude of IPP were accompanied by variations in the vertical distribution, the subsurface peak observed in the 1959/60 was not present in the 2000 s. The mechanism behind this change was undetermined but could have included changes in stratification, mixing or surface distribution of water masses as well as methodological differences. Over Hanna Shoal, the phytoplankton surface bloom now occurs earlier by several weeks compared to 1993, linked to increases in light due to earlier sea- ice retreat. In 1993 with sea ice still present in the region the surface bloom occurred in August, in 2002 and 2004 this same period was characterized by open water and low surface PP and strong subsurface production. This dataset provides a region-wide quantification of IPP and decadal trends and highlights the need for a cooperative monitoring program to observe the long-term impacts of climate change in the Arctic ecosystem.

These days, with the planet warming, carbon is the sexy element in the news. But silicon is the second most abundant element in the Earth's crust and silicate rocks comprise the majority of the mass of the Earth. However, few people (even biogeochemists) if asked could tell you in detail why silica matters to Earth's delicate balance and its inhabitants. Did you know that microbial life originated on Earth about 4 billion years ago in part because of silicate minerals or that weathering of silicate minerals saves our planet from a runaway greenhouse effect? Silica Stories is a book about the importance of silica in the evolution of life, humans, and the environment as a whole. It also makes us realize how we humans have drastically affected silica cycling and weathering everywhere on the surface of the planet, and it gives an appreciation of the astonishingly large impact that these changes have on our very existence. The authors, De La Rocha and Conley, are biogeochemists with a tremendous combined knowledge of silicon and silica, and their love for their favorite element is evident throughout the book. The book is a delight to read. It combines technical explanations with entertaining and often humorous writing. Neither a textbook nor a novel, it describes the science of silica in a compelling narrative. The authors communicate what the layperson might call “dry and complicated science” in easy-to-understand “stories.” Few people are able to do so. We scientists are well trained to communicate effectively among ourselves, but many of us fail miserably trying to help our friends or grandparents understand why we do what we do and why they should care. I cannot say with total confidence that general readers will find this book as compelling as I did, but I think it is undoubtedly a skillful attempt to reach audiences with minimal technical expertise, ranging from amateur science enthusiasts to beginning graduate students. (Admittedly some high school math and chemistry knowledge is required to fully understand certain parts of the book.) The stories are organized in 10 chapters that range widely, including the role of silica in the origin of life on Earth, the impact of tools made of silicate rocks in the evolution of human dexterity and intelligence, the “magic” electricity given off by silica crystals, the intricacies and beauty of silica biological structures, the impact of a silica-devoid diet for humans and animals, the effects of agriculture and river dams on the silica cycle, and the critical role of silica weathering in keeping the Earth cool over geological time scales. Chapter 2 was one of my favorites. It provides a fascinating description of how silica minerals, through their reactions with dissolved silica, warm water, and carbon dioxide, are key in the production of organic matter that can explain the formation of the first cellular metabolism on the early Earth. As a phytoplankton enthusiast, I may be biased but another one of my favorites was the story of “Glass Houses and Nanotechnology” in Chapter 5, where the authors describe the marvelous structural designs created in silica by microscopic organisms, such as diatoms, radiolarians, and choanoflagellates, and macroscopic life forms, such as grasses and sponges. And most remarkably these organisms precipitate silica out of solution at ambient temperatures (even in cold polar environments), while if we want to make a glass (silica) vase, we have to use temperatures in excess of 1500 °C to melt quartz. Nanotechnologists foresee creating porous silica structures just like those naturally made glass houses for a variety of uses (including medicine), although they still have a long way to go to mimic the amazing capabilities of nature. The book ends with an enlightening chapter on the role of weathering of silicate rocks in maintaining a habitable Earth in the past, present, and potentially in the future through geo-engineering. Simply put, silicate minerals continuously react with carbon dioxide, producing carbonate and bicarbonate ions, which helps reduce global warming. And this is nothing new; as the authors describe, the reaction—which has been ongoing for billions of years—has prevented runaway greenhouse effects at different times in Earth history, such as during the Paleocene-Eocene Thermal Maximum. If you feel like me, by the end of the book, you will agree with the authors that “Silica is your friend.” And you will have the sense that silica does not give up on us. Despite the efforts we humans have made through history to throw the silica cycle (and the whole planet) out of whack, silica weathering will relentlessly keep helping us by sustaining a habitable planet, although silica will take its own (geological) time to do so. Thumbs up for silica!