Biogeosciences最新文献

{"title":"Alkalinity biases in CMIP6 Earth system models and implications for simulated CO₂ drawdown via artificial alkalinity enhancement","authors":"Claudia Hinrichs, Peter Köhler, Christoph Völker, Judith Hauck","doi":"10.5194/bg-20-3717-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3717-2023","url":null,"abstract":"Abstract. The partitioning of CO2 between atmosphere and ocean depends to a large degree not only on the amount of dissolved inorganic carbon (DIC) but also on alkalinity in the surface ocean. That is also why ocean alkalinity enhancement (OAE) is discussed as one potential approach in the context of negative emission technologies. Although alkalinity is thus an important variable of the marine carbonate system, little knowledge exists on how its representation in models compares with measurements. We evaluated the large-scale alkalinity distribution in 14 CMIP6 Earth system models (ESMs) against the observational data set GLODAPv2 and show that most models, as well as the multi-model mean, underestimate alkalinity at the surface and in the upper ocean and overestimate it in the deeper ocean. The decomposition of the global mean alkalinity biases into contributions from (i) physical processes (preformed alkalinity), which include the physical redistribution of biased alkalinity originating from the soft tissue and carbonates pumps; (ii) remineralization; and (iii) carbonate formation and dissolution showed that the bias stemming from the physical redistribution of alkalinity is dominant. However, below the upper few hundred meters the bias from carbonate dissolution can gain similar importance to physical biases, while the contribution from remineralization processes is negligible. This highlights the critical need for better understanding and quantification of processes driving calcium carbonate dissolution in microenvironments above the saturation horizons and implementation of these processes into biogeochemical models. For the application of the models to assess the potential of OAE to increase ocean carbon uptake, a back-of-the-envelope calculation was conducted with each model's global mean surface alkalinity, DIC, and partial pressure of CO2 in seawater (pCO2) as input parameters. We evaluate the following two metrics: (1) the initial pCO2 reduction at the surface ocean after alkalinity addition and (2) the uptake efficiency (ηCO2) after air–sea equilibration is reached. The relative biases of alkalinity versus DIC at the surface affect the Revelle factor and therefore the initial pCO2 reduction after alkalinity addition. The global mean surface alkalinity bias relative to GLODAPv2 in the different models ranges from −85 mmol m−3 (−3.6 %) to +50 mmol m−3 (+2.1 %) (mean: −25 mmol m−3 or −1.1 %). For DIC the relative bias ranges from −55 mmol m−3 (−2.6 %) to 53 mmol m−3 (+2.5 %) (mean: −13 mmol m−3 or −0.6 %). All but two of the CMIP6 models evaluated here overestimate the Revelle factor at the surface by up to 3.4 % and thus overestimate the initial pCO2 reduction after alkalinity addition by up to 13 %. The uptake efficiency, ηCO2, then takes into account that a higher Revelle factor and a higher initial pCO2 reduction after alkalinity addition and equilibration mostly compensate for each other, meaning that resulting DIC differences in th","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135437369","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Technical note: Skirt chamber – an open dynamic method for the rapid and minimally intrusive measurement of greenhouse gas emissions from peatlands","authors":"Frederic Thalasso, Brenda Riquelme, Andrés Gómez, Roy Mackenzie, Francisco Javier Aguirre, Jorge Hoyos-Santillan, Ricardo Rozzi, Armando Sepulveda-Jauregui","doi":"10.5194/bg-20-3737-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3737-2023","url":null,"abstract":"Abstract. We present a reliable and robust open dynamic chamber for measuring greenhouse gas exchange in peatlands with minimal disturbance of the ground. This chamber, called the “skirt chamber”, is based on a transparent plastic film placed above an open frame made of sparse interwoven wires and expanded around the base of the chamber below a steel chain that ensures contact to the ground, avoiding damage, trenching, and cutting vegetation. Gas exchange is determined using a portable gas analyzer from a mass balance in which the imperfect sealing of the chamber to the ground is quantified through the injection of a methane pulse. The method was tested on a pristine peatland dominated by Sphagnum magellanicum located on Navarino Island in the subantarctic Magellanic ecoregion in Chile. Our results indicate that the skirt chamber allowed the determination of methane fluxes and ecosystem respiration in about 20 min, with a limit of detection of 0.185 mg CH4 m−2 h−1 and 173 mg CO2 m−2 h−1, respectively. We conclude that the skirt chamber is a minimally intrusive, fast, portable, and inexpensive method that allows the quantification of greenhouse gas emissions with high spatial resolution in remote locations and without delay.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"22 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135437517","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reviews and syntheses: Understanding the impacts of peatland catchment management on dissolved organic matter concentration and treatability","authors":"Jennifer Williamson, Chris Evans, Bryan Spears, Amy Pickard, Pippa J. Chapman, Heidrun Feuchtmayr, Fraser Leith, Susan Waldron, Don Monteith","doi":"10.5194/bg-20-3751-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3751-2023","url":null,"abstract":"Abstract. In the UK, most large reservoirs constructed for public water supply are in upland areas. Many are situated in catchments characterised by organic-rich soils, including peatlands. Although these soils naturally leach large amounts of dissolved organic matter (DOM) to water, the widespread degradation of upland peat in the UK is believed to have exacerbated rates of DOM loss. High and rising DOM concentrations in these regions raise treatment challenges for the water industry. In the UK, water companies are increasingly considering whether upland-catchment peat restoration measures can slow down or even reverse rising source water DOM concentrations and, thus, reduce the need for more costly and complex engineering solutions. There remains considerable uncertainty around the effectiveness of such measures, and a comprehensive overview of the research in this area remains lacking. Here, we review the peer-reviewed evidence of the effectiveness of four catchment management options in controlling DOM release from peat soils: ditch blocking, revegetation, reducing forest cover and cessation of managed burning. Results of plot-scale investigations into the effects of ditch blocking on DOM leaching are currently largely equivocal, while there is a paucity of information regarding impacts at spatial scales of more direct relevance to water managers. There is some, although limited, evidence that the terrestrial vegetation type may influence DOM concentrations and treatability. The presence of plantation forestry on peat soils is generally associated with elevated DOM concentrations, although reducing forest cover appears to have little short-term benefit, and associated disturbance may even increase concentrations further. Catchment management measures have rarely been monitored with downstream water quality as the focus. To mitigate the uncertainty surrounding restoration effects on DOM, measures should be undertaken on a site-specific basis, where the scale, effect size and duration of the intervention are considered in relation to subsequent biogeochemical processing that occurs in the reservoir, the treatment capacity of the water treatment works and future projected DOM trends.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135396423","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Canopy gaps and associated losses of biomass – combining UAV imagery and field data in a central Amazon forest","authors":"Adriana Simonetti, Raquel Fernandes Araujo, Carlos Henrique Souza Celes, Flávia Ranara da Silva e Silva, Joaquim dos Santos, Niro Higuchi, Susan Trumbore, Daniel Magnabosco Marra","doi":"10.5194/bg-20-3651-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3651-2023","url":null,"abstract":"Abstract. Understanding mechanisms of tree mortality and the dynamics of associated canopy gaps is relevant for robust estimates of carbon balance in forests. We combined monthly RGB images acquired from an unoccupied aerial vehicle with field surveys to identify gaps in an 18 ha plot installed in an old-growth central Amazon forest. We measured the size and shape of gaps and analyzed their temporal variation and correlation with rainfall over a period of 28 months. We further described associated modes of tree mortality (i.e., snapping, uprooting and standing dead) and branch fall and quantified associated losses of biomass. In total, we detected 32 gaps either in the images or field ranging in area from 9 to 835 m2. Relatively small gaps (< 39 m2) opened by branch fall were the most frequent (11 gaps). Out of 18 gaps for which both field and image data were available, three could not be detected remotely. Gaps observed in the field but not captured on the imagery were relatively small and mainly formed by the fall of branches from live and standing dead trees. Our data show that ∼ 17 % of the tree-mortality and branch-fall events only affected the lower canopy and the understory of the forest and are likely neglected by top-of-the-canopy assessments. Regardless of the detection method, the size distribution was best described by a lognormal function for gaps starting from the smallest detected size (9 and 10 m2 for field and imagery data, respectively), and the Weibull and Power functions for gaps larger than 25 m2. Properly assessing associated confidence intervals requires larger sample sizes. Repeated field measurements reveal that gap area does not differ significantly among modes of tree mortality or branch fall in central Amazon forests, with the last contributing the least to biomass loss. Predicting mechanisms of gap formation based on associated area and biomass loss remains challenging, which highlights the need for larger datasets. The rate of gap area formation was positively correlated with the frequency of extreme rainfall events, which may be related to a higher frequency of storms propagating extreme rain and wind gusts. While remote sensing has proven to be an accurate and precise method for mapping gaps compared to field data (i.e., ground truth), it is important to note that our sample size was relatively small. Therefore, the extrapolation of these results beyond our study region and landscape shall be made cautiously. Apart from improving landscape assessments of carbon balance, regional information on gap dynamics and associated mechanisms of formation are fundamental to address forest responses to altered disturbance regimes resulting from climate change.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135781268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiple nitrogen sources for primary production inferred from <i>δ</i>¹³C and <i>δ</i>¹⁵N in the southern Sea of Japan","authors":"Taketoshi Kodama, Atsushi Nishimoto, Ken-ichi Nakamura, Misato Nakae, Naoki Iguchi, Yosuke Igeta, Yoichi Kogure","doi":"10.5194/bg-20-3667-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3667-2023","url":null,"abstract":"Abstract. Carbon and nitrogen dynamics in the Sea of Japan (SOJ) are rapidly changing. In this study, we investigated the carbon and nitrogen isotope ratios of particulate organic matter (δ13CPOM and δ15NPOM, respectively) at depths of ≤100 m in the southern part of the SOJ from 2016 to 2021. δ13CPOM and δ15NPOM exhibited multimodal distributions and were classified as belonging to four classes (I–IV) according to the Gaussian mixed model. A majority of the samples were classified as class II (n=441), with a mean ± standard deviation of δ13CPOM and δ15NPOM of -23.7±1.2 ‰ and 3.1 ± 1.2 ‰, respectively. Compared to class II, class I had significantly low δ15NPOM (-2.1±0.8 ‰, n=11), class III had low δ13CPOM (-27.1±1.0 ‰, n=21), and class IV had high δ13CPOM (-20.7±0.8 ‰, n=34). All the class I samples, whose δ15NPOM showed an outlier of total datasets, were collected in winter and had a comparable temperature and salinity originating in Japanese local rivers. The generalized linear model demonstrated that the temperature and chlorophyll-a concentration had positive effects on δ13CPOM, supporting the idea that the active photosynthesis and phytoplankton growth increased δ13CPOM. However, the fluctuation in δ15NPOM was attributed to the temperature and salinity rather than nitrate concentration, which suggested that the δ15N of source nitrogen for primary production is different among the water masses. These findings suggest that multiple nitrogen sources, including nitrates from the East China Sea, Kuroshio, and Japanese local rivers, contribute to the primary production in the SOJ.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134989967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spawner weight and ocean temperature drive Allee effect dynamics in Atlantic cod, <i>Gadus morhua</i>: inherent and emergent density regulation","authors":"Anna-Marie Winter, Nadezda Vasilyeva, Artem Vladimirov","doi":"10.5194/bg-20-3683-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3683-2023","url":null,"abstract":"Abstract. Stocks of Atlantic cod, Gadus morhua, show diverse recovery responses when fishing pressure is relieved. The expected outcome of reduced fishing pressure is that the population regains its size. However, there are also cod stocks that seem to be locked in a state of low abundance from which population growth does not occur (or only slowly occurs). A plausible explanation for this phenomenon can be provided by the Allee effect, which takes place when recruitment per capita is positively related to population density or abundance. However, because of methodological limitations and data constraints, such a phenomenon is often perceived as being rare or non-existent in marine fish. In this study, we used time series of 17 Atlantic cod stocks to fit a family of population equations that consider the abundance of spawners, their body weight and sea water temperature as independent components of recruitment. The developed stock-recruitment function disentangles the effects of spawner abundance, spawner weight and temperature on recruitment dynamics and captures the diversity of density dependencies (compensation, Allee effect) of the recruitment production in Atlantic cod. The results show for 13 cod stocks an inherent spawner-abundance-related Allee effect. Allee effect strength, i.e., the relative change between maximum and minimum recruitment per capita at low abundance, was increased when recruitment production was suppressed by unfavorable changes in water temperature and/or in spawner weight. The latter can be a concomitant of heavy fishing or a result of temperature-related altered body growth. Allee effect strength was decreased when spawner weight and/or temperature elevated recruitment production. We show how anthropogenic stress can increase the risk of Allee effects in stocks where ocean temperature and/or spawner weight had been beneficial in the past but are likely to unmask and strengthen an inherent Allee effect under future conditions.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134989477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ideas and perspectives: Beyond model evaluation – combining experiments and models to advance terrestrial ecosystem science","authors":"Silvia Caldararu, Victor Rolo, Benjamin D. Stocker, Teresa E. Gimeno, Richard Nair","doi":"10.5194/bg-20-3637-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3637-2023","url":null,"abstract":"Abstract. Ecosystem manipulative experiments are a powerful tool to understand terrestrial ecosystem responses to global change because they measure real responses in real ecosystems and yield insights into causal relationships. However, their scope is limited in space and time due to cost and labour intensity. This makes generalising results from such experiments difficult, which creates a conceptual gap between local-scale process understanding and global-scale future predictions. Recent efforts have seen results from such experiments used in combination with dynamic global vegetation models, most commonly to evaluate model predictions under global change drivers. However, there is much more potential in combining models and experiments. Here, we discuss the value and potential of a workflow for using ecosystem experiments together with process-based models to enhance the potential of both. We suggest that models can be used prior to the start of an experiment to generate hypotheses, identify data needs, and in general guide experimental design. Models, when adequately constrained with observations, can also predict variables which are difficult to measure frequently or at all, and together with the data they can provide a more complete picture of ecosystem states. Finally, models can be used to help generalise the experimental results in space and time, by providing a framework in which process understanding derived from site-level experiments can be incorporated. We also discuss the potential for using manipulative experiments together with models in formalised model–data integration frameworks for parameter estimation and model selection, a path made possible by the increasing number of ecosystem experiments and diverse observation streams. The ideas presented here can provide a roadmap to future experiment–model studies.","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":"91 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135202469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Bacterioplankton dark CO2 fixation in oligotrophic waters","authors":"A. Alothman, Daffne C. López‐Sandoval, C. Duarte, S. Agustí","doi":"10.5194/bg-20-3613-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3613-2023","url":null,"abstract":"Abstract. Dark CO2 fixation by bacteria is believed to be particularly important\u0000in oligotrophic ecosystems. However, only a few studies have characterized\u0000the role of bacterial dissolved inorganic carbon (DIC) fixation in global\u0000carbon dynamics. Therefore, this study quantified the primary production\u0000(PP), total bacteria dark CO2 fixation (TBDIC fixation), and\u0000heterotrophic bacterial production (HBP) in the warm and oligotrophic Red\u0000Sea using stable-isotope labeling and cavity ring-down spectroscopy\u0000(13C–CRDS). Additionally, we assessed the contribution of bacterial DIC\u0000fixation (TBDIC %) relative to the total DIC fixation\u0000(totalDIC fixation). Our study demonstrated that TBDIC fixation increased the totalDIC fixation from 2.03 to 60.45 µg C L−1 d−1 within the photic zone, contributing 13.18 % to 71.68 % with an average value of 33.95 ± 0.02 % of the\u0000photic layer totalDIC fixation. The highest TBDIC fixation values were measured at the surface and deep (400 m) water with\u0000an average value of 5.23 ± 0.45 and\u00004.95 ± 1.33 µg C L−1 d−1, respectively. These\u0000findings suggest that the non-photosynthetic processes such as anaplerotic\u0000DIC reactions and chemoautotrophic CO2 fixation extended to the entire\u0000oxygenated water column. On the other hand, the percent of TBDIC\u0000contribution to totalDIC fixation increased as primary production\u0000decreased (R2=0.45, p<0.0001), suggesting the relevance\u0000of increased dark DIC fixation when photosynthetic production was low or\u0000absent, as observed in other systems. Therefore, when estimating the total\u0000carbon dioxide production in the ocean, dark DIC fixation must also be\u0000accounted for as a crucial component of the carbon dioxide flux in addition to\u0000photosynthesis.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49155324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fractionation of stable carbon isotopes during microbial propionate consumption in anoxic rice paddy soils","authors":"R. Conrad, P. Claus","doi":"10.5194/bg-20-3625-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3625-2023","url":null,"abstract":"Abstract. Propionate is an important intermediate during the breakdown of organic matter in anoxic flooded paddy soils. Since there are only a few experiments\u0000on carbon isotope fractionation and the magnitude of the isotopic enrichment factors (ε) involved, we measured propionate conversion\u0000to acetate, CH4 and CO2 in anoxic paddy soils. Propionate consumption was measured using samples of paddy soil from Vercelli\u0000(Italy) and the International Rice Research Institute (IRRI, the Philippines) suspended in a phosphate buffer (pH 7.0) both in the absence and\u0000presence of sulfate (gypsum) and of methyl fluoride (CH3F), an inhibitor of aceticlastic methanogenesis. Under methanogenic conditions,\u0000propionate was eventually degraded to CH4, with acetate being a transient intermediate. Butyrate was also a minor intermediate. Methane was\u0000mainly produced by aceticlastic methanogenesis. Propionate consumption was inhibited by CH3F. Butyrate and CH4 were 13C-depleted relative to propionate, whereas acetate and CO2 were 13C-enriched. The isotopic enrichment factors\u0000(εprop) of propionate consumption, determined by Mariotti plots, were in a range of −8 ‰ to −3.5 ‰. Under\u0000sulfidogenic conditions, acetate was also transiently accumulated, but CH4 production was negligible. Application of CH3F hardly\u0000affected propionate degradation and acetate accumulation. The initially produced CO2 was 13C-depleted, whereas the acetate was\u000013C-enriched. The values of εprop were −3.5 ‰. It is concluded that the degradation of organic carbon via\u0000propionate to acetate and CO2 involves only a little isotope fractionation. The results further indicate a major contribution of\u0000Syntrophobacter-type propionate fermentation under sulfidogenic conditions and Smithella-type propionate fermentation under\u0000methanogenic conditions. This interpretation is consistent with data regarding the microbial community composition published previously for the same soils.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44239282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The bottom mixed layer depth as an indicator of subsurface Chlorophyll a distribution","authors":"A. Zampollo, T. Cornulier, Rory O’Hara Murray, J. F. Tweddle, James Dunning, B. Scott","doi":"10.5194/bg-20-3593-2023","DOIUrl":"https://doi.org/10.5194/bg-20-3593-2023","url":null,"abstract":"Abstract. Primary production dynamics are strongly associated with vertical density\u0000profiles in shelf waters. Variations in the vertical structure of the\u0000pycnocline in stratified shelf waters are likely to affect nutrient fluxes and\u0000hence the vertical distribution and production rate of phytoplankton. To\u0000understand the effects of physical changes on primary production,\u0000identifying the linkage between water column density and Chlorophyll a\u0000(Chl a) profiles is essential. Here, the vertical distributions of density\u0000features describing three different portions of the pycnocline (the top,\u0000centre, and bottom) were compared to the vertical distribution of\u0000Chl a to provide auxiliary variables to estimate Chl a in shelf waters. The\u0000proximity of density features with deep Chl a maximum (DCM) was tested using\u0000the Spearman correlation, linear regression, and a major axis regression over 15\u0000years in a shelf sea region (the northern North Sea) that exhibits\u0000stratified water columns. Out of 1237 observations, 78 % reported DCM\u0000above the bottom mixed layer depth (BMLD: depth between the bottom of the\u0000pycnocline and the mixed layer underneath) with an average distance of 2.74 ± 5.21 m from each other. BMLD acts as a vertical boundary above which\u0000subsurface Chl a maxima are mostly found in shelf seas (depth ≤ 115 m).\u0000Overall, DCMs were correlated with the halfway pycnocline depth (HPD) (ρS = 0.56) which, combined with BMLD, were better predictors of the locations\u0000of DCMs than surface mixed layer indicators and the maximum squared buoyancy\u0000frequency. These results suggest a significant contribution of deep mixing\u0000processes in defining the vertical distribution of subsurface production in\u0000stratified waters and indicate BMLD as a potential indicator of the Chl a\u0000spatiotemporal variability in shelf seas. An analytical approach integrating\u0000the threshold and the maximum angle method is proposed to extrapolate BMLD,\u0000the surface mixed layer, and DCM from in situ vertical samples.\u0000","PeriodicalId":8899,"journal":{"name":"Biogeosciences","volume":" ","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48014818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}