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  • 2020-2024  (18)
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  • 1
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    Factors controlling plankton community production, export flux, and particulate matter stoichiometry in the coastal upwelling system off Peru (2020)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2023-02-08
    Description: Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The production of organic material is fueled by upwelling of nutrient-rich deep waters and high incident light at the sea surface. However, biotic and abiotic factors can modify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions of their future functioning requires understanding of the mechanisms driving the biogeochemical cycles therein. In this field experiment, we used in situ mesocosms as tools to improve our mechanistic understanding of processes controlling organic matter cycling in the coastal Peruvian upwelling system. Eight mesocosms, each with a volume of ∼55 m3, were deployed for 50 d ∼6 km off Callao (12∘ S) during austral summer 2017, coinciding with a coastal El Niño phase. After mesocosm deployment, we collected subsurface waters at two different locations in the regional oxygen minimum zone (OMZ) and injected these into four mesocosms (mixing ratio ≈1.5 : 1 mesocosm: OMZ water). The focus of this paper is on temporal developments of organic matter production, export, and stoichiometry in the individual mesocosms. The mesocosm phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. sanguinea bloom, which left a pronounced imprint on organic matter C : N : P stoichiometry. However, C, N, and P export fluxes did not increase because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, export fluxes during the study were decoupled from surface production and sustained by the remaining plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant for most of the experiment. We explain this constancy by light limitation through self-shading by phytoplankton and by inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few opportunities for blooms, which represents an event where the system becomes unbalanced. Overall, our mesocosm study revealed some key links between ecological and biogeochemical processes for one of the most economically important regions in the oceans.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Temporal dynamics of surface ocean carbonate chemistry inresponse to natural and simulated upwelling events duringthe 2017 coastal El Niño near Callao, Peru (2022)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: Oxygen minimum zones (OMZs) are characterized by enhanced carbon dioxide (CO2) levels and low pH and are being further acidified by uptake of anthropogenic atmospheric CO2. With ongoing intensification and expansion of OMZs due to global warming, carbonate chemistry conditions may become more variable and extreme, particularly in the eastern boundary upwelling systems. In austral summer (February–April) 2017, a large-scale mesocosm experiment was conducted in the coastal upwelling area off Callao (Peru) to investigate the impacts of ongoing ocean deoxygenation on biogeochemical processes, coinciding with a rare coastal El Niño event. Here we report on the temporal dynamics of carbonate chemistry in the mesocosms and surrounding Pacific waters over a continuous period of 50 d with high-temporal-resolution observations (every second day). The mesocosm experiment simulated an upwelling event in the mesocosms by addition of nitrogen (N)-deficient and CO2-enriched OMZ water. Surface water in the mesocosms was acidified by the OMZ water addition, with pHT lowered by 0.1–0.2 and pCO2 elevated to above 900 µatm. Thereafter, surface pCO2 quickly dropped to near or below the atmospheric level (405.22 µatm in 2017; Dlugokencky and Tans, 2021; NOAA/Global Monitoring Laboratory (GML)) mainly due to enhanced phytoplankton production with rapid CO2 consumption. Further observations revealed that the dominance of the dinoflagellate Akashiwo sanguinea and contamination of bird excrements played important roles in the dynamics of carbonate chemistry in the mesocosms. Compared to the simulated upwelling, natural upwelling events in the surrounding Pacific waters occurred more frequently with sea-to-air CO2 fluxes of 4.2–14.0 mmol C m−2 d−1. The positive CO2 fluxes indicated our site was a local CO2 source during our study, which may have been impacted by the coastal El Niño. However, our observations of dissolved inorganic carbon (DIC) drawdown in the mesocosms suggest that CO2 fluxes to the atmosphere can be largely dampened by biological processes. Overall, our study characterized carbonate chemistry in nearshore Pacific waters that are rarely sampled in such a temporal resolution and hence provided unique insights into the CO2 dynamics during a rare coastal El Niño event.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Nitrogen loss processes in response to upwelling in a Peruvian coastal setting dominated by denitrification – a mesocosm approach (2021)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: Upwelling of nutrient-rich deep waters make eastern boundary upwelling systems (EBUSs), such as the Humboldt Current system, hot spots of marine productivity. Associated settling of organic matter to depth and consecutive aerobic decomposition results in large subsurface water volumes being oxygen depleted. Under these circumstances, organic matter remineralisation can continue via denitrification, which represents a major loss pathway for bioavailable nitrogen. Additionally, anaerobic ammonium oxidation can remove significant amounts of nitrogen in these areas. Here we assess the interplay of suboxic water upwelling and nitrogen cycling in a manipulative offshore mesocosm experiment. Measured denitrification rates in incubations with water from the oxygen-depleted bottom layer of the mesocosms (via 15N label incubations) mostly ranged between 5.5 and 20 nmol N2 L−1 h−1 (interquartile range), reaching up to 80 nmol N2 L−1 h−1. However, actual in situ rates in the mesocosms, estimated via Michaelis–Menten kinetic scaling, did most likely not exceed 0.2–4.2 nmol N2 L−1 h−1 (interquartile range) due to substrate limitation. In the surrounding Pacific, measured denitrification rates were similar, although indications of substrate limitation were detected only once. In contrast, anammox (anaerobic ammonium oxidation) made only a minor contribution to the overall nitrogen loss when encountered in both the mesocosms and the Pacific Ocean. This was potentially related to organic matter C / N stoichiometry and/or process-specific oxygen and hydrogen sulfide sensitivities. Over the first 38 d of the experiment, total nitrogen loss calculated from in situ rates of denitrification and anammox was comparable to estimates from a full nitrogen budget in the mesocosms and ranged between ∼ 1 and 5.5 µmol N L−1. This represents up to ∼  20 % of the initially bioavailable inorganic and organic nitrogen standing stocks. Interestingly, this loss is comparable to the total amount of particulate organic nitrogen that was exported into the sediment traps at the bottom of the mesocosms at about 20 m depth. Altogether, this suggests that a significant portion, if not the majority of nitrogen that could be exported to depth, is already lost, i.e. converted to N2 in a relatively shallow layer of the surface ocean, provided that there are oxygen-deficient conditions like those during coastal upwelling in our study. Published data for primary productivity and nitrogen loss in all EBUSs reinforce such conclusion.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Response of plankton community respiration under variable simulated upwelling events (2022)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Climate change is expected to alter the intensity and frequency of upwelling in high productive coastal regions, thus impacting nutrient fluxes, primary productivity and consequently carbon cycling. However, it is unknown how these changes will impact the planktonic (phytoplankton and bacteria) community structure, which affects community respiration (CR) and hence the carbon available for sequestration or transfer to upper trophic levels. Here we present results from a 37-day mesocosm experiment where we examined the response of CR to nutrient additions by simulating upwelling events at different intensities (low, medium, high and extreme) and modes (singular and recurring additions). We also analysed the potential contribution of different plankton size classes and functional groups to CR. The trend in accumulated CR with respect to nutrient fertilisation (total nitrogen added during the experiment) was linear in the two modes. Microplankton (mostly diatoms) and nanoplankton (small flagellates) dominated under extreme upwelling intensities and high CR in both singular and recurring upwelling modes, explaining 〉65% of the observed variability in CR. In contrast, prokaryotic picoplankton (heterotrophic bacteria and autotrophic cyanobacteria) explained 〈43% of the variance in CR under the rest of the upwelling intensities and modes tested. Changes in planktonic community structure, while modulating CR variability, would regulate the metabolic balance of the ecosystem, shifting it towards net-heterotrophy when the community is dominated by small heterotrophs and to net-autotrophy when large autotrophs prevail; although depending on the mode in which nutrients are supplied to the system. This shift in the dominance of planktonic organism will hence affect not only CR but also carbon sequestration in upwelling regions
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Microzooplankton communities and their grazing of phytoplankton under artificial upwelling in the oligotrophic ocean (2023)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Ocean artificial upwelling has been suggested to boost primary production and increase harvestable resources such as fish. Yet, for this ecosystem-based approach to work, an effective energy transfer up the food web is required. Here, we studied the trophic role of microzooplankton under artificial upwelling via biomass and community composition as well as grazing rates on phytoplankton. Using mesocosms in the oligotrophic ocean, we supplied nutrient-rich deep water at varying intensities (low to high) and addition modes (a Singular large pulse or smaller Recurring pulses). Deep-water fertilization created a diatom-dominated bloom that scaled with the amount of inorganic nutrients added, but also Synechococcus -like cells, picoeukaryotes and nanophytoplankton increased in abundance with added nutrients. After 30 days, towards the end of the experiment, coccolithophores bloomed under recurring upwelling of high intensity. Across all upwelling scenarios, the microzooplankton community was dominated by ciliates, dinoflagellates (mixo- and heterotrophic) and radiolarians. Under the highest upwelling intensity, the average grazing rates of Synechococcus -like cells, picoeukaryotes and nanophytoplankton by microzooplankton were 0.35 d -1 ± 0.18 (SD), 0.09 d -1 ± 0.12 (SD), and 0.11 d -1 ± 0.13 (SD), respectively. There was little temporal variation in grazing of nanophytoplankton but grazing of Synechococcus -like cells and picoeukaryotes were more variable. There were positive correlations between abundance of these groups and grazing rates, suggesting a response in the microzooplankton community to prey availability. The average phytoplankton to microzooplankton ratio (biovolume) increased with added deep water, and this increase was highest in the Singular treatment, reaching ~30 (m 3 m -3 ), whereas the phytoplankton to total zooplankton biomass ratio (weight) increased from ~1 under low upwelling to ~6 (g g -1 ) in the highest upwelling but without a difference between the Singular and the Recurring mode. Several smaller, recurring upwelling events increased the importance of microzooplankton compared with one large pulse of deep water. Our results demonstrate that microzooplankton would be an important component for trophic transfer if artificial upwelling would be carried out at scale in the oligotrophic ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Seawater carbonate chemistry considerations for ocean alkalinity enhancement research: theory, measurements, and calculations (2023)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-01-08
    Description: Ocean alkalinity enhancement (OAE) is a proposed marine carbon dioxide removal (mCDR) approach that has the potential for large-scale uptake of significant amounts of atmospheric carbon dioxide (CO2). Removing anthropogenic legacy CO2 will be required to stabilise global surface temperatures below the 1.5–2 ∘C Paris Agreement target of 2015. In this chapter we describe the impacts of various OAE feedstocks on seawater carbonate chemistry, as well as pitfalls that need to be avoided during sampling, storage, and measurement of the four main carbonate chemistry parameters, i.e. dissolved inorganic carbon (DIC), total alkalinity (TA), pH, and CO2 fugacity (fCO2). Finally, we also discuss considerations in regard to calculating carbonate chemistry speciation from two measured parameters. Key findings are that (1) theoretical CO2 uptake potential (global mean of 0.84 mol of CO2 per mole of TA added) based on carbonate chemistry calculations is probably secondary in determining the oceanic region in which OAE would be best; (2) carbonate chemistry sampling is recommended to involve gentle pressure filtration to remove calcium carbonate (CaCO3) that might have been precipitated upon TA increase as it would otherwise interfere with a number of analyses; (3) samples for DIC and TA can be stabilised to avoid the risk of secondary CaCO3 precipitation during sample storage; and (4) some OAE feedstocks require additional adjustments to carbonate chemistry speciation calculations using available programs and routines, for instance if seawater magnesium or calcium concentrations are modified.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    OA and ripples metabolism data (2020)
    PANGAEA
    Details
    Publication Date: 2023-01-13
    Keywords: DATE/TIME; Gross primary production/Respiration rate ratio; Gross primary production of oxygen; Identification; Net calcification rate of calcium carbonate; Net community calcification rate of calcium carbonate, dark; Net community calcification rate of calcium carbonate, light; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); Respiration rate, oxygen; Treatment
    Type: Dataset
    Format: text/tab-separated-values, 216 data points
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    DATA PANGAEA
  • 8
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    Sediment topography enhances the response of coral reef carbonate sediment dissolution to ocean acidification (2020)
    PANGAEA
    Details
    Publication Date: 2023-01-13
    Description: The interaction between current flow and topography (e.g., surface ripples) in shallow, permeable coral reef carbonate sediments establishes pressure gradients that increase the rate of sediment-water solute exchange relative to fluid shear along a flat bottom. It is currently unknown how this effect from surface ripples will modify the rate at which the sediment porewater is exposed to future chemical changes in the overlying water column, such as elevated pCO2 that is causing ocean acidification (OA). To address this question, this study used a series of 22-hour incubations in flume aquaria with permeable calcium carbonate sediment communities and examined the interactive effect of pCO2 (400 and 1000 µatm) and surface topography (flat and rippled sediments) on carbonate sediment metabolism and dissolution. According to dissolved oxygen optode image analysis, the presence of surface ripples increased the oxygenated area below the sediment surface by 295% relative to flat sediments. This was reflected in the sediment-to-water column fluxes of dissolved oxygen, where rippled sediments exhibited rates of respiration (R) and gross primary production (GPP) that were ~ 45% and ~ 50% higher, respectively, than flat sediments. An increase in pCO2 shifted the sediments in the flat flumes from net calcifying (Gnet 〉 0) to net dissolving (Gnet 〈 0), an effect that was amplified an additional ~ 60% in rippled sediments. These results suggest that current estimates of coral reef carbonate sediment Gnet may be underestimating the dissolution response to OA where the carbonate sediment environment exhibits ripples in the topography.
    Type: Dataset
    Format: application/zip, 2 datasets
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    DATA PANGAEA
  • 9
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    KOSMOS 2020 Peru mesocosm study on ecosystem responses to different light and upwelling intensities: dissolved inorganic carbon concentration and total alkalinity of water samples (2023)
    PANGAEA
    Details
    Publication Date: 2023-12-06
    Description: This data is part of the BMBF project CUSCO (Coastal Upwelling Systems in a Changing Ocean). Here we report the dissolved inorganic carbon concentration and total alkalinity during a 35-day experiment, where we enclosed natural plankton communities in in-situ mesocosms off Peru. The experiment investigated the interactive effects of light and upwelling on the Humboldt upwelling ecosystem by mimicking a gradient of upwelling intensities (0%, 15%, 30%, 45% and 60%) under summer-time high light and winter-time low light. Integrated seawater samples from a depth between 0 and 10m were collected using a 5L Integrating Water sampler (IWS; Hydro-Bios, Kiel). Dissolved inorganic carbon (DIC) and total alkalinity (TA) samples were obtained by 0.2µm gentle pressure filtration, poisoned with saturated 7.5 % mercury chloride (HgCl2) solution and frozen at -20°C until measurement. Samples for Total Alkalinity (TA) were measured by means of potentiometric titration with 0.05 M HCl using an automated titration device (862 Metrohm Compact Titrosampler). All DIC samples taken until day 17 were measured using an Automated Infra-Red Inorganic Carbon Analyzer (AIRICA) with a LICOR detector (LI-7000 CO2/H20 Analyzer, MARIANDA, Kiel). Certified reference material (Dickson standard for oceanic CO2 Measurements - CRM Batch 142 with salinity = 33.389 and DIC = 2038,07 µmol/kg) was measured and used to correct measured sample values. Additional DIC samples were measured using gas chromatography-mass spectrometry (GC-MS) to determine the 13C signal. The data of the GC-MS was adjusted to the AIRICA data using a linear transformation. Missing days were filled using an average of the day before and after.
    Keywords: Alkalinity, total; AQUACOSM; Automated Infra Red Inorganic Carbon Analyzer (AIRICA), MARIANDA; with a LICOR detector (LI-7000 CO2/H2O Analyzer); Carbon, inorganic, dissolved; Coastal Upwelling System in a Changing Ocean; Comment; CUSCO; DATE/TIME; Day of experiment; Depth, water, experiment, bottom/maximum; Depth, water, experiment, top/minimum; DIC; Event label; Field experiment; Gas chromatography - Mass spectrometry (GC-MS); Humboldt Current System; KOSMOS_2020; KOSMOS_2020_Mesocosm-M1; KOSMOS_2020_Mesocosm-M10; KOSMOS_2020_Mesocosm-M2; KOSMOS_2020_Mesocosm-M3; KOSMOS_2020_Mesocosm-M4; KOSMOS_2020_Mesocosm-M5; KOSMOS_2020_Mesocosm-M6; KOSMOS_2020_Mesocosm-M7; KOSMOS_2020_Mesocosm-M8; KOSMOS_2020_Mesocosm-M9; KOSMOS Peru; light limitation; MESO; Mesocosm experiment; Mesocosm label; mesocosm study; Network of Leading European AQUAtic MesoCOSM Facilities Connecting Mountains to Oceans from the Arctic to the Mediterranean; Potentiometric titration, Metrohm 862 Compact Titrosampler; TA alkalinity; Treatment; Treatment: light condition; Type of study; Upwelling
    Type: Dataset
    Format: text/tab-separated-values, 1761 data points
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    DATA PANGAEA
  • 10
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    Oxygen and carbon fluxes from shallow unvegetated sediments in the Clarence Estuary, NSW, Australia under warming and ocean acidification conditions (2020)
    PANGAEA
    Details
    Publication Date: 2024-01-02
    Description: Dissolved organic/inorganic carbon and oxygen fluxes from whole sediment core incubations subject to temperature and ocean acidification manipulations. Estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors of warming (from Δ-3 °C to Δ+5 °C on ambient mean temperatures) and ocean acidification (OA, ~2 times the current partial pressure of CO2, pCO2) was investigated ex situ. Warming alone increased sediment heterotrophy, resulting in a proportional increase in sediment DOC uptake, with sediments becoming net sinks of DOC (3.5 to 8.8 mmol-C m-2 d-1) at warmer temperatures (Δ+3 °C and Δ+5 °C, respectively). This temperature response changed under OA conditions, with sediments becoming more autotrophic and a greater sink of DOC (1 to 4 times greater than under current-pCO2). This response was attributed to the stimulation of heterotrophic bacteria with the autochthonous production of labile organic matter by microphytobenthos. Extrapolating these results to the global area of unvegetated subtidal estuarine sediments, the future climate of warming (Δ+3 °C) and OA may decrease the estuarine export of DOC by ~80 % (~150 Tg-C yr-1) and have a disproportionately large impact on the global DOC budget.
    Keywords: AIRICA analyzer (Miranda); Australia; Carbon, inorganic, dissolved; Carbon, organic, dissolved; Clarence_Estuary; DEPTH, sediment/rock; DEPTH, water; estuaries; EXP; Experiment; LDO-probe; Ocean acidification; Oxygen saturation; pH; pH probe; Replicates; Salinity; SALINO; Salinometer; sediment; Surface area; Temperature, water; Temperature sensor; Time in minutes; Time point, descriptive; TOC analyser, Aurora 1030W; Treatment; Volume; warming
    Type: Dataset
    Format: text/tab-separated-values, 1053 data points
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    DATA PANGAEA
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