Ocean Productivity Research Articles

Oceanic Primary Production Estimation Based On Machine Learning

AbstractOceanic primary production (OPP) is crucial for ecosystem services and global carbon cycle. However, sensitivity to geographic and environmental characteristics limits the application of semi‐empirical OPP estimate models, such as the vertically generalized productivity model (VGPM) and its modified version, particularly in coastal regions. In addition, the difficulty in collecting necessary parameters also hampers long‐term OPP estimates. Data‐driven machine learning (ML) methods can automatically capture the relationships between the input parameters and the objective; hence, they may become new methods for global OPP estimates. In this study, the effectiveness of ML methods to estimate OPP and the key attributes influencing ML performance in different regions and seasons are discussed. First, the ML models obtain a lower root mean square error than the VGPM and Eppley‐VGPM. In addition, the random forest (RF) model achieves the best performance among the four selected ML models. The enhancement in the accuracy of OPP estimates based on the RF model is more obvious in coastal regions than in the open ocean. In the four seasons, the RF model obtains better estimates of OPP than the Eppley‐VGPM, especially for summer. Moreover, input attributes, including sea surface temperature (SST), photosynthetic active radiation (PAR), and chlorophyll‐a concentration (Chlor‐a), achieve the best performance. The suitable alternative input attributes are SST/Chlor‐a in the coastal regions, and single Chlor‐a, SST/Chlor‐a, and PAR/Chlor‐a in the open ocean. Except for the SST/PAR/Chlor‐a combination, input with Chlor‐a, that is, SST/Chlor‐a and PAR/Chlor‐a, result a relatively acceptable performance in the four seasons.

Carbon In, Carbon Out: Balancing the Ocean’s Books

Scientists have developed a consensus guide of standard protocols for how best to measure oceanic primary productivity, a key component in Earth’s carbon cycle.

Differential response of chlorophyll-a concentrations to explosive volcanism in the western South Pacific

When it is deposited in the ocean, volcanic ash has the potential to release iron and other nutrients into surface water to stimulate ocean productivity. In the western South Pacific Ocean (SPO), one of the most important volcanic ash deposition regions, occasional widespread transport of volcanic ash may supply the nutrients not only locally around source islands but also within the wider the western SPO, accompanied by phytoplankton response. Through a comparative analysis of satellite and reanalysis data for the past 19 years (2004–2022), this study reveals that four explosive volcanic eruptions, Rabaul volcano, Papua New Guinea (October, 2006), Ambae volcano, Vanuatu (July, 2018), Ulawun volcano, Papua New Guinea (June, 2019), and Hunga volcano, Tonga (January, 2022), had the most strong stratospheric injection (>15 km) and mass loading of volcanic materials over the wider the western SPO (covering an area of >765,000 km2). The transport of 2006, 2018, 2019 volcanic emissions, was not likely associated with significant ash deposition over the western SPO. However, the Hunga eruption led to the deposition of ash-laden volcanic plumes over a wide area (~2,000 km from source), and was followed by the increase in chlorophyll-a concentrations (Chl-a) in the region (~70% increase). Minor changes related to other nutrient sources (e.g., hydrothermal input) suggest a link between the increase in Chl-a and 2022 Hunga ash falls over the western SPO. Our results indicate that volcanic ash deposition has implications for phytoplankton productivity in the western SPO, and highlights the need for further research into understanding how nutrient supply alleviated limitations of phytoplankton at the community level.

Comparison of bacterial carbon production estimates from dilution and 3H‐leucine methods across a strong gradient in ocean productivity

AbstractThe uptake of 3H‐labeled leucine into proteins, a widely used method for estimating bacterial carbon production (BCP), is suggested to underestimate or overestimate bacterial growth in the open ocean by a factor of 40 uncertainty. Meanwhile, an alternative BCP approach, by the dilution method, has untested concerns about potential overestimation of bacterial growth from dissolved substrates released by filtration. We compared BCPDil and BCPLeu estimates from three cruises across a broad trophic gradient, from offshore oligotrophy to coastal upwelling, in the California Current Ecosystem. Our initial analyses based on midday microscopical estimates of bacterial size and a priori assumptions of conversions relationships revealed a mean two‐fold difference in BCP estimates (BCPDil higher), but no systematic bias between low and high productivity stations. BCPDil and BCPLeu both demonstrated strong relationships with bacteria cell abundance. Reanalysis of results, involving a different cell carbon‐biovolume relationship and informed by forward angle light scatter from flow cytometry as a relative cell size index, demonstrated that BCPDil and BCPLeu are fully compatible, with a 1 : 1 fit for bacteria of 5 fg C cell−1. Based on these results and considering different strengths of the methods, the combined use of 3H‐labeled leucine and dilution techniques provide strong mutually supportive constraints on bacterial biomass and production.

Enhanced Monsoon‐Driven Upwelling in Southeast Asia During the Little Ice Age

AbstractClimate change impacts ocean nutrient availability and will likely alter the marine food web. While climate models predict decreased average ocean productivity, the extent of these changes, especially in the marginal seas upon which large human populations depend, is not well understood. Here, we reconstructed changes in seawater phosphate concentration and nitrate source over the past 400 years, which reveals a more than 50% decline in residence time of seawater phosphate, and 8%–48% decline in subsurface nitrogen supply following the coldest period of Little Ice Age. Our data indicates a link between surface ocean nutrient supply and the East Asian Summer Monsoon strength in an economically important marginal sea. As climate models predict that the East Asian Summer monsoon will strengthen in the future, our study implies that surface ocean primary productivity may increase in the South China Sea, contrary to the predicted decrease in global average ocean productivity.

Biogeochemical Argo Floats Reveal the Evolution of Subsurface Chlorophyll and Particulate Organic Carbon in Southeast Indian Ocean Eddies

AbstractEddies modulate open ocean productivity, and this influence depends on both eddy source and evolution. Southeast Indian Ocean eddies are important pathways for the westward transport of biogeochemical anomalies from the Leeuwin current into the central oligotrophic South Indian Ocean (SIO). Eddy processes at the base of the mixed layer may stimulate and sustain phytoplankton, allowing these eddy impacts to persist over thousands of kilometers. We present 4 months of high‐frequency profiles from autonomous floats in one anticyclonic and one cyclonic eddy in the SIO. At the start of observations, from September to October, particulate organic carbon (POC) and especially chlorophyll were higher in the cyclone, and evenly distributed throughout the mixed layers in both eddies. As spring progressed and the eddies were transported westward, chlorophyll and POC concentrated at the base of the mixed layer at depths invisible to satellites, likely reflecting nutrient depletion in overlying waters. In the anticyclone, the increased chlorophyll at depth occurred as POC decreased, suggesting photo‐acclimation and thus both light and nutrient stress. In contrast, in the cyclone chlorophyll to POC ratios remained close to constant as their subsurface maxima formed. In both eddies, the subsurface biomass maxima exhibited no significant change in oxygen saturation state over several months suggesting these communities are sustained by low ongoing productivity in balance with community respiration. Thus, deep biomass layers may represent a mechanism for long‐distance transfer of eddy plankton communities which is not reflected in satellite remote sensing.

A mutant fitness assay identifies bacterial interactions in a model ocean hot spot

Bacteria that assemble in phycospheres surrounding living phytoplankton cells metabolize a substantial proportion of ocean primary productivity. Yet the type and extent of interactions occurring among species that colonize these micron-scale "hot spot" environments are challenging to study. We identified genes that mediate bacterial interactions in phycosphere communities by culturing a transposon mutant library of copiotrophic bacterium Ruegeria pomeroyi DSS-3 with the diatom Thalassiosira pseudonana CCMP1335 as the sole source of organic matter in the presence or absence of other heterotrophic bacterial species. The function of genes having significant effects on R. pomeroyi fitness indicated explicit cell-cell interactions initiated in the multibacterial phycospheres. We found that R. pomeroyi simultaneously competed for shared substrates while increasing reliance on substrates that did not support the other species' growth. Fitness outcomes also indicated that the bacterium competed for nitrogen in the forms of ammonium and amino acids; obtained purines, pyrimidines, and cofactors via crossfeeding; both initiated and defended antagonistic interactions; and sensed an environment with altered oxygen and superoxide levels. The large genomes characteristic of copiotrophic marine bacteria are hypothesized to enable responses to dynamic ecological challenges occurring at the scale of microns. Here, we discover >200 nonessential genes implicated in the management of fitness costs and benefits of membership in a globally significant bacterial community.

Distinct tectono-magmatism on the margins of Rodinia and Gondwana

The orogenic petrological processes associated with the amalgamation of Rodinia (ca. 1 Ga) and Gondwana (ca. 550 Ma) reflect distinct tectonic dynamics that might have contributed to the contrasting geochemical and biological evolution following the orogenies. In this study, we explore these differences using the time sequence analysis of geochemical proxies in the detrital zircons sourced from the margin of East Gondwana. The zircon Eu anomalies are stronger during the formation of Gondwana than Rodinia, indicating a thicker Gondwana crust than Rodinia; the hinterland of Rodinia (∼35 km) is significantly thinner than its core Grenville Province (55–60 km). The Ce to U and Ti ratio, U/Yb, and εHf(t) proxies suggest that the Rodinia assembly was dominated by non-arc intraplate magmatism, consistent with widespread high-temperature magmatism and protracted granulite-facies metamorphism. The thin crust and accordingly, low-elevation terrain, possibly overriding an anomalously hot mantle, limited continental weathering flux, and primary productivity in the Mesoproterozoic oceans. By contrast, the orogenies leading to the assembly of Gondwana may have proceeded in a modern-style plate tectonic manner, resulting in rapid uplift at the Gondwana margin, where voluminous clastic sediments were subsequently recycled and contributed to the post-orogenic magmatism from ca. 500 Ma. This massive crustal reworking is reflected by negative εHf(t) values of zircons that contrast εHf(t)∼0 in the Mesoproterozoic. The emergence of extensive mountains accelerated erosion and delivered key nutrients that might have fueled the rapid diversification of life forms in the late Precambrian and early Paleozoic.

Oceanic primary production estimation based on machine learning

Oceanic primary production estimation based on machine learning

Prokaryotic community dynamics and nitrogen-cycling genes in an oxygen-deficient upwelling system during La Niña and El Niño conditions.

Dissolved oxygen regulates microbial distribution and nitrogen cycling and, therefore, ocean productivity and Earth's climate. To date, the assembly of microbial communities in relation to oceanographic changes due to El Niño Southern Oscillation (ENSO) remains poorly understood in oxygen minimum zones (OMZ). The Mexican Pacific upwelling system supports high productivity and a permanent OMZ. Here, the spatiotemporal distribution of the prokaryotic community and nitrogen-cycling genes was investigated along a repeated transect subjected to varying oceanographic conditions associated with La Niña in 2018 and El Niño in 2019. The community was more diverse during La Niña and in the aphotic OMZ, dominated by the Subtropical Subsurface water mass, where the highest abundances of nitrogen-cycling genes were found. The largest proportion of the Gulf of California water mass during El Niño provided warmer, more oxygenated, and nutrient-poor waters towards the coast, leading to a significant increase of Synechococcus in the euphotic layer compared with the opposite conditions during La Niña. These findings suggest that prokaryotic assemblages and nitrogen genes are linked to local physicochemical conditions (e.g. light, oxygen, nutrients), but also to oceanographic fluctuations associated with ENSO phases, indicating the crucial role of climate variability in microbial community dynamics in this OMZ.

Did nutrient-rich oceans fuel Earth’s oxygenation?

Abstract Phosphorus (P) availability exerts a strong influence on primary productivity in global oceans. However, its abundance and role as a limiting nutrient prior to the start of the Great Oxygenation Event (GOE) 2.45–2.32 Ga is unclear. Low concentrations of seawater P have been proposed to explain the apparent delay between the early appearance of oxygen-producing Cyanobacteria and the onset of atmospheric oxygenation. We report evidence for seawater precipitation of Ca-phosphate nanoparticles in 2.46–2.40 Ga iron formations deposited on a marine shelf, including shallow-water facies, immediately prior to the onset of the GOE. Our modeling shows that the co-precipitation of Ca-phosphate and ferrous silicate (greenalite) required ferruginous seawater with dissolved P concentrations many orders of magnitude higher than in today’s photic zone. If correct, it follows that P availability is unlikely to have suppressed the expansion of Cyanobacteria prior to the GOE. A reservoir of P-rich surface water shortly before 2.40 Ga could ultimately have triggered a rapid rise in atmospheric oxygen by fueling a sharp increase in primary productivity and organic-carbon burial. We speculate that the enigmatic Lomagundi positive carbon-isotope excursion, recorded in 2.32–2.06 Ga shallow-water carbonates, may mark a key step in the transition toward a modern biosphere of high biological productivity controlled by nutrient availability.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Monthly Ocean Primary Productivity Forecasting by Joint Use of Seasonal Climate Prediction and Temporal Memory

Ocean primary productivity generated by phytoplankton is critical for ocean ecosystems and the global carbon cycle. Accurate ocean primary productivity forecasting months in advance is beneficial for marine management. Previous persistence-based prediction studies ignore the temporal memories of multiple relevant factors and the seasonal forecasting skill drops quickly with increasing lead time. On the other hand, the emerging ensemble climate forecasts are not well considered as new predictability sources of ocean conditions. Here we proposed a joint forecasting model by combining the seasonal climate predictions from ten heterogeneous models and the temporal memories of relevant factors to examine the monthly predictability of ocean productivity from 0.5- to 11.5-month lead times. The results indicate that a total of ~90% and ~20% productive oceans are expected to be skillfully predicted by the combination of seasonal SST predictions and local memory at 0.5- and 4.5-month leads, respectively. The joint forecasting model improves by 10% of the skillfully predicted areas at 6.5-month lead relative to the prediction by productivity persistence. The hybrid data-driven and model-driven forecasting approach improves the predictability of ocean productivity relative to individual predictions, of which the seasonal climate predictions contribute largely to the skill improvement over the equatorial Pacific and Indian Ocean. These findings highlight the advantages of the integration of climate predictions and temporal memory for ocean productivity forecasting and may provide useful seasonal forecasting information for ocean ecosystem management.

Light Under Arctic Sea Ice in Observations and Earth System Models

AbstractThe intensity and spectrum of light under Arctic sea ice, key to the energy budget and primary productivity of the Arctic Ocean, are tedious to observe. Earth System Models (ESMs) are instrumental in understanding the large‐scale properties and impacts of under‐ice light. To date, however, ESM parameterizations of radiative transfer have been evaluated with a few observations only. From observational programs conducted over the past decade at four locations in the Northern Hemisphere sea ice zone, 349 observational records of under‐ice light and coincident environmental characteristics were compiled. This data set was used to evaluate seven ESM parameterizations. Snow depth, melt pond presence and, to some extent, ice thickness explain the observed variance in light intensity, in agreement with previous work. The effects of Chlorophyll‐a are also detected, with rather low intensity. The spectral distribution of under‐ice light largely differs from typical open ocean spectra but weakly varies among the 349 records except for a weak effect of snow depth on the blue light contribution. Most parameterizations considered reproduce variations in under‐ice light intensity. Large errors remain for individual records, on average by a factor of ∼3, however. Skill largely improves if more predictors are considered (snow and ponds in particular). Residual errors are attributed to missing physics in the parametrizations, inconsistencies in the model‐observation comparison protocol, and measurement errors. We provide recommendations to improve the representation of light under sea ice in the ice‐ocean model NEMO, which may also apply to other ESMs and help improve next‐generation ESMs.

Combined effects of microplastics and warming enhance algal carbon and nitrogen storage

Algae dominate primary production in groundwater and oceans and play a critical role in global carbon dioxide fixation and climate change but are threatened by ongoing global warming events (such as heatwaves) and increasing microplastic (MP) pollution. However, whether and how ecologically important phytoplankton respond to the combined effects of warming and MPs remain poorly understood. We thus investigated the combined effects of these factors on carbon and nitrogen storage and the mechanisms underlying the alterations in the physiological performance of a model diatom, Phaeodactylum tricornutum, exposed to a warming stressor (25 °C compared with 21 °C) and polystyrene MP acclimation. Although warmer conditions decreased the cell viability, the diatoms subjected to the synergistic effects of MPs and warming showed significant increases in the growth rate (1.10-fold) and nitrogen uptake rate (1.26-fold). Metabolomics and transcriptomic analyses revealed that MPs and warming mainly promoted fatty acid metabolism, the urea cycle, glutamine and glutamate production, and the tricarboxylic acid (TCA) cycle due to an increased level of 2-oxoglutarate, which is the hub of carbon and nitrogen metabolism and accounts for the acquisition and utilization of carbon and nitrogen. Our findings emphasize the nonnegligible effects of MPs and HWs on the algal carbon and nitrogen cycles in waters.

Decadal decline in maternal body condition of a Southern Ocean capital breeder

The changing physical properties of the Southern Ocean are known to impact the recruitment and survival of Antarctic krill (Euphausia superba). For oceanic krill predators, the resulting reduced energy intake may lead to population-level effects likely preceded by an alteration in the animals’ body condition. This is especially true for capital breeders that rely on stored energy for successful reproduction. One such Southern Ocean capital breeder, the southern right whale (Eubalaena australis), has been monitored over the past 43 years in their South African wintering ground. Changes in the population have been documented in the past decade, including a decreased reproductive rate and a shift in foraging strategy. To evaluate if a reduced foraging success is an underlying factor, we assessed the temporal variation in morphological body condition through aerial photogrammetry. Results showed a 23% reduction in maternal body condition, potentially contributing to the decreased reproductive rate of the population. To the best of our knowledge, this is the first study to quantify a decadal reduction in the body condition of a capital breeder dependent on Southern Ocean productivity. Understanding the bioenergetic consequences of environmental change is vital to predicting species’ resilience to climate change.

Emissions of Nitric Oxide from Photochemical and Microbial Processes in Coastal Waters of the Yellow and East China Seas.

Nitric oxide (NO) is an atmospheric pollutant and climate forcer as well as a key intermediary in the marine nitrogen cycle, but the ocean's NO contribution and production mechanisms remain unclear. Here, high-resolution NO observations were conducted simultaneously in the surface ocean and the lower atmosphere of the Yellow Sea and the East China Sea; moreover, NO production from photolysis and microbial processes was analyzed. The NO sea-air exchange showed uneven distributions (RSD = 349.1%) with an average flux of 5.3 ± 18.5 × 10-17 mol cm-2 s-1. In coastal waters where nitrite photolysis was the predominant source (89.0%), NO concentrations were remarkably higher (84.7%) than the overall average of the study area. The NO from archaeal nitrification accounted for 52.8% of all microbial production (11.0%). We also examined the relationship between gaseous NO and ozone which helped identify sources of atmospheric NO. The sea-to-air flux of NO in coastal waters was narrowed by contaminated air with elevated NO concentrations. These findings indicate that the emissions of NO from coastal waters, mainly controlled by reactive nitrogen inputs, will increase with the reduced terrestrial NO discharge.

Primary production in the North Atlantic estimated from in situ water column data observed by Argo floats and remote sensing

Combining information on the vertical distribution of nutrients and remote sensing can potentially improve estimates of ocean primary production (PP). Here, we employ in situ observations of chlorophyll a and nitrate from biogeochemical Argo floats deployed in the North Atlantic together with remote sensing to estimate PP and compare these results to estimates based on model approaches not including vertically resolved nutrient distributions. Analysis of the float data shows chlorophyll a distribution relates closely to both nutricline depth and latitude, and these relationships can be explained by nutrient and light availability. PP estimates based on satellite and Argo-observations also relate to both latitude and nutrient distributions. An analysis of these float-based PP estimates shows that large-scale patterns of total water column PP and associated variability are consistent with expected photosynthetic responses to different combinations of light and nutrient availability. When PP-estimates based solely on surface observations were plotted against light and nutrient fields, significant structural differences emerged compared with estimates that included subsurface observations, in particular in oligotrophic areas and areas with a shallow nutricline. The combination of in situ water column observations with remote sensing potentially opens a new phase in the estimation of ocean primary production.

Mapping amorphous SiO2 in Devonian shales and the possible link to marine productivity during incipient forest diversification

Silica cycling in the world’s oceans is not straightforward to evaluate on a geological time scale. With the rise of radiolarians and sponges from the early Cambrian onward, silica can have two depositional origins, continental weathering, and biogenic silica. It is critical to have a reliable method of differentiating amorphous silica and crystalline silica to truly understand biogeochemical and inorganic silica cycling. In this study, opal-A is mapped across the Western Canada Sedimentary Basin in the Late Devonian Duvernay Formation shales using longwave hyperspectral imaging alongside geochemical proxies that differentiate between crystalline and amorphous SiO2, during the expansion of the world’s early forests. Signaled by several carbon isotope excursions in the Frasnian, the punctata Event corresponds to the expansion of forests when vascular land plants develop seeds and deeper root networks, likely resulting in increased pedogenesis. Nutrients from thicker soil horizons entering the marine realm are linked to higher levels of primary productivity in oceans and subsequent oxygen starvation in deeper waters at this time. The results of this study reveal, for the first time, the spatial distribution of amorphous SiO2 across a sedimentary basin during this major shift in the terrestrial realm when forests expand and develop deeper root networks.

Large mass strandings of selected odontocete species: statistics, locations, and relation to earth processes

Larger mass strandings of open ocean odontocetes (toothed whales) of 10+ animals are examined with a compilation of 710 worldwide events. Sixspecies form 96% of events (false killer, long-finned pilot, melon-headed, short-finned pilot, sperm and white whales), with beaked, killer, andpygmy killer whales forming 4%. Site type was determined for 630 events – three-quarters (76%) are in bays, 14% in shallow topographicallycomplex areas (estuarine environments, straits, keys, reef and coastal lagoons), 8% on relatively unindented coasts, with ice entrapment (of killerwhales) and miscellaneous categories being 2%. For the 76% of events in bays, sites with headland-bay character make up 42%, spit-bays 20%(even though there are only four of them), indented bays 9% and unspecified bay types 5%. Headland-bays and spit-bays become stranding sitesthrough the properties endowed them by their mechanisms of formation and maintenance, but these mechanisms differ greatly for the two.Breakwaters, groyne series, tides, partial burial, and violent storms also appear as themes. Nearshore slopes are less than 1° for 94 of 105 siteshaving bathymetry information, with only two reaching or exceeding 3°. Some types of potential stranding sites can be identified by simplequantitative specifications for planform, sediment size, and seabed slope, although strandings will not necessarily occur there. There is an indicationthat larger strandings are globally correlated with areas of higher oceanic primary productivity near landmasses and oceanic islands, but quantitativestudies are needed to clarify any such possible relationship. There is also an indication that larger strandings are associated with plate tectonics,with few events being seen on the steeper swell resistant active western margins of South America and South Island (New Zealand) in particular.In contrast several larger events are recorded for the relatively older passive margins of the south-eastern sides of these two landmasses, putativelybecause waves and swell have had time to construct stranding sites on them. Similarly, few larger events are seen for steeper shores adjacent tocoastal highlands, such as those of South Africa and Brazil. These observations indicate previously unsuspected relations between the phenomenonof odontocete mass strandings and global scale earth and ocean processes, but they are essentially hypotheses in need of more quantitativeexamination.