Hawaii Ocean Time-series Research Articles

Niche differentiation in microorganisms capable of using alternative reduced nitrogen sources studied across depth and between oxic and anoxic ocean regions

IntroductionAssimilation of reduced nitrogen is less energetically costly than assimilation of oxidized forms. In the open ocean, ammonium is generally absent from the water column, including in oxygen-deficient zones (ODZs). Some microorganisms can use alternative organic reduced nitrogen forms like urea and cyanate, as indicated by the presence of cyanase (cynS) and urease (ureC) genes.MethodsHere we examine the Hawaii Ocean Time series, two stations in the Eastern Tropical South Pacific ODZ and one in the Eastern Tropical North Pacific ODZ, using phylogenetic read placement of metagenomic reads to define the proportion of each taxon capable of using cyanate and/or urea in oxic and anoxic environments.ResultsAn improved phylogenetic tree found that Thioglobaceae and Verrucomicrobia had the capability to use urea. Our detailed examination of all the microbial groups able to use cyanate and urea illuminated that niche differentiation, an adaptation to minimize competition, determines chosen nitrogen sources, partitioning by depth and oxygen. Urease genes were found in Picocyanobacteria and SAR11 in surface waters, Thaumarchaeota and Nitrospina in deep waters, Thioglobaceae and Cand. Scalindua in ODZs, and Verrucomicrobia in the deep oxycline. In the ODZs, the percentage of Anammox bacteria that contained cynS was double that of those containing ureC, and their cynS transcripts were abundant, indicating a preference for cyanate over urea.DiscussionWhile Prochlorococcus could utilize cyanate in the deep chlorophyll maximum, in the ODZs, Prochlorococcus uses nitrite rather than compete with Cand. Scalindua for cyanate, even though cyanate is present. SAR11 and Prochlorococcus may compete for urea in surface waters, but for SAR11, the presence of ureC was negatively correlated with nitrate concentration (p = 10−17), with ~ 40% of SAR11 genomes containing the ureC gene in oxic surface waters but none at depth, indicating that SAR11 bacteria switched to using nitrate when available. In the oxycline above the ODZ, where Thaumarchaeota and Nitrospina both could use urea, 50% of Nitrospina were also able to use cyanate, and their cyanase transcripts were present. This use of dissolved organic N should allow a higher biomass of N-cycling microbes and higher N-transformation rates than in a system competing for ammonia only.

Programmable flow injection: a versatile technique for benchtop and autonomous analysis of phosphate and silicate in seawater

High-resolution, autonomous monitoring of phosphate and silicate in the marine environment is essential to understand their complex dynamics and implications for the functioning of marine ecosystems. In the absence of dependable reagent-less sensors for these nutrients, leveraging established colorimetric techniques using miniaturized analyzers, such as programmable Flow Injection (pFI), offers the best immediate solution to meet oceanographic accuracy and precision standards. In this work, we further optimize the phosphomolybdate and silicomolybdate assays recently adapted for use with pFI, laying the groundwork for the technique’s use for long-term, autonomous operations. For both assays, we show that only a narrow range of acidities and molybdate concentrations can maximize sensitivity while minimizing salt effects. In addition, we demonstrate the stability of our optimized colorimetric reagent formulations, ensuring that analytical sensitivity remains within 10% of initial levels for at least 35 days of continuous use. We then applied our optimized protocols to produce oceanographically consistent phosphate and silicate profiles at the Hawaii Ocean Time Series (HOTS) and Southern Ocean Time Series (SOTS), respectively, which compared favorably against a reference method and historical data. Using certified reference materials for nutrients in seawater, we show that our pFI protocols, optimized for long-term operations, achieve a shipboard precision better than 6% and a relative combined uncertainty (k=1) of 4.5% for phosphate (0.45 - 2.95 µmol L-1) and 6.2% for silicate (2.2 to 103 µmol L-1). To demonstrate pFI’s potential as a versatile tool for autonomous monitoring, we report a five-day hourly phosphate time series at a coastal shore station in central California (n=121 analyses), examine phosphate uptake by seaweed at five-minute intervals at a seaweed aquaculture facility (n=103), and discuss a unique, high-resolution surface silicate transect spanning multiple frontal zones in the Australian sector of the Southern Ocean (n=249). These data, obtained using a commercially available pFI analyzer, confirm that pFI is a viable technology for autonomous monitoring of phosphate and silicate, paving the way for more ambitious, long-term deployments in a variety of settings.

Evaluation of three contrasting models in estimating primary production from ocean color remote sensing using long-term time-series data at oceanic and coastal sites

Accurate estimates of depth-integrated Net Primary Production (NPP, mg C m−2 d−1) and the creation of a robust climate data record of NPP for the global oceans are essential goals of the ocean color remote sensing community. Here, we take advantage of in situ NPP measurements from three long-term time-series sites, the HOT (Hawaii Ocean Time-series), BATS (Bermuda Atlantic Time-series Study) and CARIACO (Ocean Time-Series Program from the Cariaco basin), spanning over 30 years to evaluate three contrasting models in estimating NPP from ocean color remote sensing. These models for NPP estimation include the Absorption-based Model (AbPM), which relies on phytoplankton absorption coefficient, the Vertically Generalized Production Model (VGPM), which centers on chlorophyll-a concentration, and the Carbon-based Productivity Model (CbPM) centering on phytoplankton carbon. In addition to the accuracy of NPP estimation from these models, we laid great emphasis on evaluating their skills in capturing the monthly to seasonal variations and interannual trends in NPP at the three sites. Comparison with in situ NPP at all three long-term sites (∼20 years) showed that AbPM yielded the highest coefficient of determination (R2 = 0.67) and the lowest uncertainties (Bias = 0.03 and unbiased root mean square difference = 0.17). Seasonal and interannual variations apparent in the in situ NPP time-series records were best captured by AbPM. These results showcase the robust capabilities of AbPM and its superiority for global carbon cycling and climate change studies, largely because it takes into account optical and photosynthetic parameters of local phytoplankton.

Increased cyanophage infection at the bottom of the euphotic zone, especially in the fall.

Picocyanobacteria contribute greatly to offshore primary production with cells extending through the deep euphotic zone. Literature indicates high viral infection of cyanobacteria in ocean transition zones. We postulate that the bottom of the euphotic zone is a transition zone, where communities transition from phototrophic to aphotic processes. We use single-copy core genes to examine cyanophage to cyanobacteria ratios in cellular metagenomes in the subtropical North Atlantic and Pacific. Cyanophage to cyanobacteria terL/rpoB ratios generally increase to >10 in the deep euphotic zone. As light levels decrease in the fall, Prochlorococcus in the deep euphotic zone experience reduced light levels. We find clear differences between spring (Geotraces GA02) and fall (GA03) in the North Atlantic, with terL/rpoB ratios increasing to >40 in the fall. When examining 23 months of the North Pacific Hawaii Ocean Timeseries, the depth of elevated cyanophage to cyanobacteria ratios in cellular metagenomes negatively correlated with surface photosynthetic radiation (PAR), particularly with the change in PAR, which reflected the season. In fall, all picocyanobacteria ecotypes were found at depths enriched with viruses, while in summer, only low light ecotypes were affected. Thus, we find high cyanophage infection both in the deep euphotic zone and during seasonal transitions.

Quantifying Net Community Production and Calcification at Station ALOHA Near Hawai'i: Insights and Limitations From a Dual Tracer Carbon Budget Approach

AbstractA budget approach is used to disentangle drivers of the seasonal mixed layer carbon cycle at Station ALOHA (A Long‐term Oligotrophic Habitat Assessment) in the North Pacific Subtropical Gyre (NPSG). The budget utilizes data from the WHOTS (Woods Hole—Hawaii Ocean Time‐series Site) mooring, and the ship‐based Hawai'i Ocean Time‐series (HOT) in the NPSG, a region of significant oceanic carbon uptake. Parsing the carbon variations into process components allows an assessment of both the proportional contributions of mixed layer carbon drivers and the seasonal interplay of drawdown and supply from different processes. Annual net community production reported here is at the lower end of previously published data, while net community calcification estimates are 4‐ to 7‐fold higher than available sediment trap data, the only other estimate of calcium carbonate export at this location. Although the observed seasonal cycle in dissolved inorganic carbon in the NPSG has a relatively small amplitude, larger fluxes offset each other over an average year. Major supply comes from physical transport, especially lateral eddy transport throughout the year and entrainment in the winter, offset by biological carbon uptake in the spring. Gas exchange plays a smaller role, supplying carbon to the surface ocean between Dec‐May and outgassing in Jul‐Oct. Evaporation‐precipitation (E‐P) is variable with precipitation prevailing in the first half and evaporation in the second half of the year. The observed total alkalinity signal is largely governed by E‐P with a somewhat stronger net calcification signal in the wintertime.

Nitrogen Fixation in Mesoscale Eddies of the North Pacific Subtropical Gyre: Patterns and Mechanisms

AbstractMesoscale eddies have been shown to support elevated dinitrogen (N2) fixation rates (NFRs) and abundances of N2‐fixing microorganisms (diazotrophs), but the mechanisms underlying these observations are not well understood. We sampled two pairs of mesoscale cyclones and anticyclones in the North Pacific Subtropical Gyre in 2017 and 2018 and compared our observations with seasonal patterns from the Hawaii Ocean Time‐series (HOT) program. Consistent with previous reports, we found that NFRs were anomalously high for this region (up to 3.7‐fold above previous monthly HOT observations) in the centers of both sampled anticyclones. In 2017, these elevated rates coincided with high concentrations of the diazotroph Crocosphaera. We then coupled our field‐based observations, together with transcriptomic analyses of nutrient stress marker genes and ecological models, to evaluate the role of biological (via estimates of growth and grazing rates) and physical controls on populations of Crocosphaera, Trichodesmium, and diatom symbionts at the mesoscale. Our results suggest that increased Crocosphaera abundances in the 2017 anticyclone resulted from the alleviation of phosphate limitation, allowing cells to grow at rates exceeding grazing losses. In contrast, distributions of larger, buoyant taxa (Trichodesmium and diatom symbionts) appeared less affected by eddy‐driven biological controls. Instead, they appeared driven by physical dynamics along frontal boundaries that separate cyclonic and anticyclonic eddies. No examined controls were able to explain our 2018 findings of higher NFRs in the anticyclone. A generalized explanation of elevated NFRs in mesoscale eddies remains challenging due to the interplay of eddy‐driven bottom‐up, top‐down, and physical control mechanisms.

Nutrient uptake plasticity in phytoplankton sustains future ocean net primary production.

Annually, marine phytoplankton convert approximately 50 billion tons of dissolved inorganic carbon to particulate and dissolved organic carbon, a portion of which is exported to depth via the biological carbon pump. Despite its important roles in regulating atmospheric carbon dioxide via carbon sequestration and in sustaining marine ecosystems, model-projected future changes in marine net primary production are highly uncertain even in the sign of the change. Here, using an Earth system model, we show that frugal utilization of phosphorus by phytoplankton under phosphate-stressed conditions can overcompensate the previously projected 21st century declines due to ocean warming and enhanced stratification. Our results, which are supported by observations from the Hawaii Ocean Time-series program, suggest that nutrient uptake plasticity in the subtropical ocean plays a key role in sustaining phytoplankton productivity and carbon export production in a warmer world.

Genome Sequence of the Euphotic Hawaiian Gammaproteobacterium HetDA_MAG_MS8, in the Order Nevskiales, Family Oceanococcaceae, Genus Oceanococcus.

We present a metagenome-assembled genome (MAG), HetDA_MAG_MS8, that was determined to be unique via relative evolutionary divergence (RED) scores and average nucleotide identity (ANI) values. HetDA_MAG_MS8 is in the order Nevskiales, genus Oceanococcus, and was assembled from a heterocytous cyanobiont enrichment from the Hawaii Ocean Time Series. HetDA_MAG_MS8 is predicted to be a facultative, aerobic, anoxygenic photolithoheterotroph that has the potential for sulfide oxidation and dimethylsulfoniopropionate (DMSP) synthesis.

Fragility of marine photosynthesis

Ecosystem fragility is an often used term in oceanography yet to this day it lacks a precise and widely accepted definition. Defining and subsequently quantifying fragility would be of great value, for such measures could be used to objectively ascertain the level of risk marine ecosystems face. Risk assessments could further be used to define the level of protection a given ocean region requires from economic activity, such as fisheries. With this aim we introduce to the oceanographic literature the concepts of marginal production and fragility, which we define for marine photosynthesis, the base of the oceanic food web. We demonstrate that marine photosynthesis is always fragile with respect to light, implying variability in surface irradiance acts unfavourably on biomass. We also demonstrate that marine photosynthesis can be both fragile and antifragile with respect to the mixed-layer depth, implying variability in mixed-layer depth can act both favourably and unfavourably on biomass. Quantification of marginal production and fragility is presented on data from two open ocean stations: Hawaii Ocean Time Series and Bermuda Atlantic Time-Series Study. Seasonal cycle of biomass is modelled and the effects of primary production fragility are analysed. A new tipping point for marine phytoplankton is identified in the form of a depth horizon. Using the new definitions presented here a rich archive of data can be used straightforwardly to quantify primary production fragility. The definitions can also be used to predict when primary production enters the fragile state during the seasonal cycle.

Modelling the effects of copepod diel vertical migration and community structure on ocean carbon flux using an agent-based model

Fecal pellets are a significant component of total particulate organic carbon (POC) flux in the ocean and a key component of the biological pump. The effect of copepod community structure, feeding behavior, and diel vertical migration (DVM) on fecal pellet carbon flux was investigated using an agent-based model, which was applied to two contrasting open ocean regions: an oligotrophic (Hawaii Ocean Time-series site ALOHA) and a mesotrophic (Japanese time-series site K2) system. Data from the VERtical Transport in the Global Ocean (VERTIGO) project was used to parameterize the model, and modelled fecal pellet fluxes were compared to field-derived neutrally buoyant sediment trap data to examine how community structure and DVM impact fecal pellet carbon flux in the water column. The model produces copepod fecal pellet fluxes that are consistent with sediment trap data from K2 and ALOHA and with other modeling studies. The vertical distribution of copepods matching nighttime field data resulted in a greater magnitude of fecal pellet flux at all model depths compared to daytime distributions. Communities dominated by omnivores resulted in higher fecal pellet carbon flux and lower POC attenuation than those dominated by carnivores or detritivores. Incorporating DVM into the simulations produced lower fecal pellet fluxes in some cases, while also marginally improving the agreement between the modeled and observed median fecal pellet fluxes. The relatively simplified model presented here shows that an agent-based model that uses trait-based relationships for physiological rates can be used to give insight into the variability of particle flux in the deep ocean.

An analysis of protists in Pacific oxygen deficient zones: implications for Prochlorococcus and N2 -producing bacteria.

Ocean oxygen deficient zones (ODZs) host 30%-50% of marine N2 production. Cyanobacteria photosynthesizing in the ODZ create a secondary chlorophyll maximum and provide organic matter to N2 -producing bacteria. This chlorophyll maximum is thought to occur due to reduced grazing in anoxic waters. We first examine ODZ protists with long amplicon reads. We then use non-primer-based methods to examine the composition and relative abundance of protists in metagenomes from the Eastern Tropical North and South Pacific ODZs and compare these data to the oxic Hawaii Ocean Time-series (HOT) in the North Pacific. We identify and quantify protists in proportion to the total microbial community. From metagenomic data, we see a large drop in abundance of fungi and protists such as choanoflagellates, radiolarians, cercozoa and ciliates in the ODZs but not in the oxic mesopelagic at HOT. Diplonemid euglenozoa were the only protists that increased in the ODZ. Dinoflagellates and foraminifera reads were also present in the ODZ though less abundant compared to oxic waters. Denitrification has been found in foraminifera but not yet in dinoflagellates. DNA techniques cannot separate dinoflagellate cells and cysts. Metagenomic analysis found taxonomic groups missed by amplicon sequencing and identified trends in abundance.

Cyclonic eddies modulate temporal and spatial decoupling of particulate carbon, nitrogen, and biogenic silica export in the North Pacific Subtropical Gyre

AbstractMesoscale eddies may enhance nutrient injection into the photic zone and ultimately the magnitude and composition of particle export to depth. Using satellite altimetry, we identified 38 cyclonic eddies that passed in close proximity to the Hawaii Ocean Time‐series (HOT) Station ALOHA, located in the North Pacific Subtropical Gyre, from 1993 to 2018. Particulate carbon (C), nitrogen (N), and biogenic silica (Si) export rates, measured using free floating sediment traps deployed at 150 m as part of HOT, were then associated with either the eddy core or edge based on distance to the eddy center and time of eddy evolution. Elemental fluxes varied significantly within and among individual eddies depending on season and eddy age. Spatially, biogenic Si fluxes were enhanced relative to particulate C and N fluxes at both the cores and edges, with temporally highest particulate C, N and biogenic Si fluxes occurring during the mature stage (3–8 weeks). On average, biogenic Si fluxes were 200 ± 80% (30–270% increase) higher relative to non‐eddy and during non‐bloom periods, with modest enhanced particulate C (10–30% increase) and N (10–20% increase) fluxes. In contrast, during the bloom season (July and August), elemental fluxes were all reduced by 20% relative to non‐eddy references, suggesting that cyclonic eddies depress export during the bloom period. Our results indicate that cyclonic eddies not only increase, but differentially impact the sinking export of critical biological elements, thereby contributing to long term ecological changes in foodwebs that rely on silica as well as carbon for growth.

Reconciling Between Optical and Biological Determinants of the Euphotic Zone Depth

AbstractThe conventional use of optically determined 1% of surface photosynthetically available radiation (PAR) depth (Z1%PAR, λ = 400–700 nm) as a metric for the euphotic zone depth (Zeu) has been a matter of debate for several decades because of frequent inconsistencies with the base of euphotic zone determined biologically, that is, the compensation depth (Zc). In this study, we attempt to reconcile between optical and biological determinants of the euphotic zone through the use of a large data set of coincidental profiles of downwelling irradiance and primary production. These measurements cover open ocean waters in the tropics, subtropics, temperate regions, and from two time‐series stations, the Hawaii Ocean Time‐series (HOT) and the Bermuda Atlantic Time‐series Study (BATS). We report that, at least for these measurements, Z1%PAR is too shallow (by 14.1%) compared to Zc, while Z0.1%PAR is too deep (by 32.7%). Further, the irradiance at Zc (i.e., the compensation irradiance, Ic) varies by a factor of more than five, but its ratio to surface irradiance is relatively stable. In general, Ic corresponds to 0.48 ± 0.23% of surface PAR, or 0.87 ± 0.40% of surface usable solar radiation (USR, for λ = 400–560 nm), or 1.50 ± 0.67% of surface downwelling irradiance at 490 nm. These results suggest that Z0.5%PAR, or Z0.9%USR, or Z1.5%490 could be promising alternatives to bridge the optical and biological determinants of the euphotic zone depths for waters in the open ocean at low to middle latitudes.

Change of coral carbon isotopic response to anthropogenic Suess effect since around 2000s

The stable carbon isotope composition (δ13C) in coral skeletons can be used to reconstruct the evolution of the dissolved inorganic carbon (DIC) in surface seawater, and its long-term declining trend during the past 200 years (~1800–2000) reflects the effect of anthropogenic Suess effect on carbonate chemistry in surface oceans. The global atmospheric CO2 concentration still has been increasing since 2000, and the Suess effect is intensifying. Considering the coral's ability of resilience and acclimatization to external environmental stressors, the response of coral δ13C to Suess effect may change and needs to be re-evaluated. In this study, ten long coral δ13C time series synthesized from different oceans were used to re-evaluate the response of coral carbonate chemistry to Suess effect under the changing environments. These δ13C time series showed a long-term declining trend since 1960s, but the declining rates slowed in eight time series since around 2000s. Considering that the declining rates of the DIC-δ13C in surface seawater from the Hawaii Ocean Time-series Station and Bermuda Atlantic Time-series Station has not changed since 2000 compared with those during 1960–1999, the change in the coral δ13C trends at eight of ten locations may indicate that the response of coral δ13C to the anthropogenic Suess effect has changed since around 2000s. This change may have resulted from coral acclimatization to external environmental stressors. To adapt to acidifying oceans, coral may have the ability to regulate the source of DIC in extracellular calcifying fluid and/or the utilization way of DIC, therefore the response of coral δ13C to anthropogenic Suess effect will change accordingly.

Quantifying the Atmospheric CO2 Forcing Effect on Surface Ocean pCO2 in the North Pacific Subtropical Gyre in the Past Two Decades

Despite the well-recognized importance in understanding the long term impact of anthropogenic release of atmospheric CO2 (its partial pressure named as pCO2air) on surface seawater pCO2 (pCO2sw), it has been difficult to quantify the trends or changing rates of pCO2sw driven by increasing atmospheric CO2 forcing (pCO2swatm_forced) due to its combination with the natural variability of pCO2sw (pCO2swnat_forced) and the requirement of long time series data records. Here, using a novel satellite-based pCO2sw model with inputs of ocean color and other ancillary data between 2002 and 2019, we address this challenge for a mooring station at the Hawaii Ocean Time-series Station in the North Pacific subtropical gyre. Specifically, using the developed pCO2sw model, we differentiated and separately quantified the interannual-decadal trends of pCO2swnat_forced and pCO2swatm_forced. Between 2002 and 2019, both pCO2sw and pCO2air show significant increases at rates of 1.7 ± 0.1 μatm yr–1 and 2.2 ± 0.1 μatm yr–1, respectively. Correspondingly, the changing rate in pCO2swnat_forced is mainly driven by large scale forcing such as Pacific Decadal Oscillation, with a negative rate (-0.5 ± 0.2 μatm yr–1) and a positive rate (0.6 ± 0.3 μatm yr–1) before and after 2013. The pCO2swatm_forced shows a smaller increasing rate of 1.4 ± 0.1 μatm yr–1 than that of the modeled pCO2sw, varying in different time intervals in response to the variations in atmospheric pCO2. The findings of decoupled trends in pCO2swatm_forced and pCO2swnat_forced highlight the necessity to differentiate the two toward a better understanding of the long term oceanic absorption of anthropogenic CO2 and the anthropogenic impact on the changing surface ocean carbonic chemistry.

Ecosystem implications of fine-scale frontal disturbances in the oligotrophic ocean – An idealized modeling approach

In the subtropical ocean, physical and biogeochemical patchiness exists across a range of spatial and temporal scales. As ocean surface temperatures rise, climate models suggest that the strength of the basin-scale biological carbon pump may diminish due to increased stratification and depleted surface nutrients. However, global model predictions often cannot account for climate-physical-ecosystem interactions occurring at finer spatial scales (e.g., less than a few tens of kilometers). In order to study such fine-scale interactions, we developed a computationally tractable, idealized modeling framework that allows for a systematic assessment of the impact of fine-scale frontal disturbances (i.e., short-lived upwelling and downwelling events) on biogeochemical and ecosystem dynamics. The model successfully captured both the mean dynamics and the range of ecosystem variability observed at the Hawaii Ocean Time-series (HOT) site in the oligotrophic North Pacific Subtropical Gyre. Fine-scale frontal disturbances were shown to impact both phytoplankton assemblages and carbon cycling. Specifically, disturbances of shorter duration but higher intensity favored the growth of large phytoplankton and contributed to elevated carbon export efficiency. However, for disturbances of longer duration and higher intensity, a decoupling between physical changes and biological responses led to a reduced utilization efficiency of upwelled nutrients and thus a reduction in new production. Our results emphasize that future changes in both large and fine-scale physical dynamics may play an important role in shaping marine ecosystems, and could be accounted for in the next-generation global climate models using this type of parameterization.

Message from the Executive Director Interview with Dave Hambright, Editor‐in‐Chief, Limnology and Oceanography

Message from the Executive Director Interview with Dave Hambright, Editor‐in‐Chief, <i>Limnology and Oceanography</i>

SeaFlow data v1, high-resolution abundance, size and biomass of small phytoplankton in the North Pacific

SeaFlow is an underway flow cytometer that provides continuous shipboard observations of the abundance and optical properties of small phytoplankton (<5 μm in equivalent spherical diameter, ESD). Here we present data sets consisting of SeaFlow-based cell abundance, forward light scatter, and pigment fluorescence of individual cells, as well as derived estimates of ESD and cellular carbon content of picophytoplankton, which includes the cyanobacteria Prochlorococcus, Synechococcus and small-sized Crocosphaera (<5 μm ESD), and picophytoplankton and nanophytoplankton (2–5 μm ESD). Data were collected in surface waters (≈5 m depth) from 27 oceanographic cruises carried out in the Northeast Pacific Ocean between 2010 and 2018. Thirteen cruises provide high spatial resolution (≈1 km) measurements across 32,500 km of the Northeast Pacific Ocean and 14 near-monthly cruises beginning in 2015 provide seasonal distributions at the long-term sampling site (Station ALOHA) of the Hawaii Ocean Time-Series. These data sets expand our knowledge of the current spatial and temporal distributions of picophytoplankton in the surface ocean.

Autonomous seawater &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and pH time series from 40 surface buoys and the emergence of anthropogenic trends

Abstract. Ship-based time series, some now approaching over 3 decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean carbon dioxide (CO2) uptake and biogeochemical processes. Advancements in autonomous marine carbon sensors and technologies over the last 2 decades have led to the expansion of observations at fixed time series sites, thereby improving the capability of characterizing sub-seasonal variability in the ocean. Here, we present a data product of 40 individual autonomous moored surface ocean pCO2 (partial pressure of CO2) time series established between 2004 and 2013, 17 also include autonomous pH measurements. These time series characterize a wide range of surface ocean carbonate conditions in different oceanic (17 sites), coastal (13 sites), and coral reef (10 sites) regimes. A time of trend emergence (ToE) methodology applied to the time series that exhibit well-constrained daily to interannual variability and an estimate of decadal variability indicates that the length of sustained observations necessary to detect statistically significant anthropogenic trends varies by marine environment. The ToE estimates for seawater pCO2 and pH range from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 time series, Woods Hole Oceanographic Institution Hawaii Ocean Time-series Station (WHOTS) in the subtropical North Pacific and Stratus in the South Pacific gyre, have been deployed longer than the estimated trend detection time and, for these, deseasoned monthly means show estimated anthropogenic trends of 1.9±0.3 and 1.6±0.3 µatm yr−1, respectively. In the future, it is possible that updates to this product will allow for the estimation of anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https://doi.org/10.7289/V5DB8043 and https://www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html (Sutton et al., 2018).

Editorial: Long‐term studies in limnology and oceanography

We use a variety of approaches and techniques to study aquatic ecosystems. Among the most powerful of these are studies that involve repeated measurements of the same variables over longer periods (i.e., many years to decades). The reason for this is that changes in our streams, rivers, lakes, wetlands, estuaries, and oceans may take place and are only observable over prolonged periods. Consequently, we need systematic and sustained environmental monitoring to document the effects of global change on aquatic ecosystems and understand its causes and consequences. The case that long-term research is instrumental in advancing scientific knowledge and policy was made in two recent publications entitled, “Long-term studies contribute disproportionately to ecology and policy” (Hughes et al. 2017. Bioscience) and “Long-term research in ecology and evolution: a survey of challenges and opportunities” (Kuebbing et al. 2018. Ecological Monographs). These papers found that long-term studies are cited more, are more likely to be published in highly regarded scientific journals, and play a larger role in shaping environmental policy. Despite this, long-term studies constitute a small fraction of aquatic science research. From my quick survey, only 5–6% of publications on lakes, oceans, estuaries, and rivers include long-term data collections (data from Clarivate Analytics Web of Science for papers published between 1981 and 2018). Is long-term monitoring vital for aquatic sciences and should we be doing more of these studies? I think so. There are many examples where continuous time-series documented ecosystem change and allowed for stakeholders and decision makers to work together to reduce or fix the problem. Acid rain provides perhaps one of the most famous examples of the value of long-term research. A series of measurements in northeast U.S.A., eastern Canada, and Europe demonstrated declining pH in rain, snow, and water that resulted in measurable impacts on lake ecosystems. Another example of the value of long-term data collection are the continuing observations of atmospheric levels of carbon dioxide (CO2) at the Mauna Loa Observatory in Hawaii which eventually provided clues about the changing global climate. Coupled to the atmospheric CO2 records are 30 years of rising seawater partial pressure CO2 measurements at nearby station ALOHA, which have been accompanied by simultaneous increases in ocean acidity. It can take many years to see the benefits of long-term data collection. Unfortunately, long-term studies are chronically underfunded in many countries and can be difficult to sustain through multiple grant cycles. Granting agencies generally promote research that provides immediate tangible products and benefits and typically fund studies for limited durations (1–5 years). Compounding this funding problem is the issue that many of us do a poor job of explaining the necessity and importance of long-term research to the public. Even among our peers, the value of long-term research can be a tough sell. I recently asked two of my Canadian colleagues to review one of my grant applications, which included the prospect of long-term research. Although one of my colleagues encouraged me to increase the long-term monitoring facet of my proposal, the other one was more critical. It was suggested to me to de-emphasize this aspect of my proposal because of the perception that the review panel would not consider it novel and would hesitate to allocate public research dollars to long-term monitoring research. Altogether, we must do better to promote long-term studies and the many benefits that they provide. Not only can a long-term time-series generate unique knowledge, but it can also lead to the discovery of surprise findings. We should support our peers through their long-term research endeavors and remind our politicians and funding agencies that long-term studies are essential to the creation of effective environmental policy. This past year, we at Limnology and Oceanography celebrated the anniversaries of two long-term monitoring research sites with the creation of two virtual issues; the 30th Anniversary of the Hawaii Ocean Time-series (https://aslopubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)1939-5590.ALOHA30) and the 50th Anniversary of the Experimental Lakes Area (https://aslopubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)1939-5590.ELA50?campaign=dartwol|4795815320). We are finishing the year with this capstone special issue on long-term perspectives in aquatic research. But let us not end there. I hope to see more long-term studies published in Limnology and Oceanography.