ALBERT

Description: The data is from a mesocosm experiment set up outside Lima, Peru to study the influence of upwelling of oxygen minimum zone (OMZ) water. The mesocosm bags were 2 m in diameter and extended from the surface down to 19 m depth, where the last 2 m was a conical sediment trap. Eight mesocosm bags were used and they were moored at 12.0555°S; 77.2348°W just north of Isla San Lorenzo where the water depth is ~30 m. The experiment was started 25 February 2017 by closing the mesocosm bags and were run for 50 days. Two treatments were used (water with different OMZ signature), each with four replicates. Water (100 m3) from the OMZ was collected from two locations and depths. The first was collected from 12.028323°S; 77.223603°W from 30 m depth, and the second one from 12.044333°S; 77.377583°W from 70 m depth. The original aim was to collect severe and moderate OMZ signature water (differing in e.g. nitrate concentrations) from the first and second site, respectively. This assumption was based on long-term monitoring data, however, the chemical properties (e.g. nitrate concentration) was more similar in these water masses than anticipated, rather reflecting low and very low OMZ signatures from site 1 and 2 respectively. To have a baseline of measured variables, the mesocosms where closed and environmental and biological variables were determined over 10 days. After this period, the OMZ water was added to the mesocosms in two steps on day 11 and 12 after the enclosure of the mesocosms. As the mesocosms contain a specific volume (~54 m3), the process of adding the OMZ water started with first removing water from the mesocosms. The water removed (~20 m3) was pumped out from 11-12 m depth. A similar volume of OMZ water, from both collection sites, was then pumped into four replicate mesocosms each. The OMZ water was pumped into the mesocosms moving the input hose between 14-17 m depth. The water collected at 30 m depth was pumped into mesocosms M1, M4, M5 and M8 having a low OMZ signature and water from 70 m depth into mesocosms M2, M3, M6 and M7 having a very low OMZ signature. Due a halocline at 12 m depth (see below), the added OMZ water was not immediately mixed throughout the mesocosm bag. Sampling took place every second day over a period of 50 days, and all variables were taken with an integrated water sampler (HydroBios, IWS) pre-programed to fill from 0 – 10 m depth and all samples consisted of this integrated samples from the upper 10 m. The samples were stored dark in cool boxes and brought back to the laboratory and processed right away. Sampling took place in the morning, and the samples were usually back in the laboratory around noon. Measured variables included inorganic nutrients, dissolved organic nutrients, extracellular enzyme activity: leucine aminopeptidase (LAP) and alkaline phosphatase activity (APA), and the phytoplankton and bacterial community composition.

Description: The data is from a mesocosm experiment set up outside Lima, Peru to study the influence of upwelling of oxygen minimum zone (OMZ) water. The mesocosm bags were 2 m in diameter and extended from the surface down to 19 m depth, where the last 2 m was a conical sediment trap. Eight mesocosm bags were used and they were moored at 12.0555°S; 77.2348°W just north of Isla San Lorenzo where the water depth is ~30 m. The experiment was started 25 February 2017 by closing the mesocosm bags and were run for 50 days. Two treatments were used (water with different OMZ signature), each with four replicates. Water (100 m3) from the OMZ was collected from two locations and depths. The first was collected from 12.028323°S; 77.223603°W from 30 m depth, and the second one from 12.044333°S; 77.377583°W from 70 m depth. The original aim was to collect severe and moderate OMZ signature water (differing in e.g. nitrate concentrations) from the first and second site, respectively. This assumption was based on long-term monitoring data, however, the chemical properties (e.g. nitrate concentration) was more similar in these water masses than anticipated, rather reflecting low and very low OMZ signatures from site 1 and 2 respectively. To have a baseline of measured variables, the mesocosms where closed and environmental and biological variables were determined over 10 days. After this period, the OMZ water was added to the mesocosms in two steps on day 11 and 12 after the enclosure of the mesocosms. As the mesocosms contain a specific volume (~54 m3), the process of adding the OMZ water started with first removing water from the mesocosms. The water removed (~20 m3) was pumped out from 11-12 m depth. A similar volume of OMZ water, from both collection sites, was then pumped into four replicate mesocosms each. The OMZ water was pumped into the mesocosms moving the input hose between 14-17 m depth. The water collected at 30 m depth was pumped into mesocosms M1, M4, M5 and M8 having a low OMZ signature and water from 70 m depth into mesocosms M2, M3, M6 and M7 having a very low OMZ signature. Due a halocline at 12 m depth (see below), the added OMZ water was not immediately mixed throughout the mesocosm bag. Sampling took place every second day over a period of 50 days, and all variables were taken with an integrated water sampler (HydroBios, IWS) pre-programed to fill from 0 – 10 m depth and all samples consisted of this integrated samples from the upper 10 m. The samples were stored dark in cool boxes and brought back to the laboratory and processed right away. Sampling took place in the morning, and the samples were usually back in the laboratory around noon. Measured variables included inorganic nutrients, dissolved organic nutrients, extracellular enzyme activity: leucine aminopeptidase (LAP) and alkaline phosphatase, and the phytoplankton and bacterial community composition.

Description: The data is from a mesocosm experiment set up outside Lima, Peru to study the influence of upwelling of oxygen minimum zone (OMZ) water. The mesocosm bags were 2 m in diameter and extended from the surface down to 19 m depth, where the last 2 m was a conical sediment trap. Eight mesocosm bags were used and they were moored at 12.0555°S; 77.2348°W just north of Isla San Lorenzo where the water depth is ~30 m. The experiment was started 25 February 2017 by closing the mesocosm bags and were run for 50 days. Two treatments were used (water with different OMZ signature), each with four replicates. Water (100 m3) from the OMZ was collected from two locations and depths. The first was collected from 12.028323°S; 77.223603°W from 30 m depth, and the second one from 12.044333°S; 77.377583°W from 70 m depth. The original aim was to collect severe and moderate OMZ signature water (differing in e.g. nitrate concentrations) from the first and second site, respectively. This assumption was based on long-term monitoring data, however, the chemical properties (e.g. nitrate concentration) was more similar in these water masses than anticipated, rather reflecting low and very low OMZ signatures from site 1 and 2 respectively. To have a baseline of measured variables, the mesocosms where closed and environmental and biological variables were determined over 10 days. After this period, the OMZ water was added to the mesocosms in two steps on day 11 and 12 after the enclosure of the mesocosms. As the mesocosms contain a specific volume (~54 m3), the process of adding the OMZ water started with first removing water from the mesocosms. The water removed (~20 m3) was pumped out from 11-12 m depth. A similar volume of OMZ water, from both collection sites, was then pumped into four replicate mesocosms each. The OMZ water was pumped into the mesocosms moving the input hose between 14-17 m depth. The water collected at 30 m depth was pumped into mesocosms M1, M4, M5 and M8 having a low OMZ signature and water from 70 m depth into mesocosms M2, M3, M6 and M7 having a very low OMZ signature. Due a halocline at 12 m depth (see below), the added OMZ water was not immediately mixed throughout the mesocosm bag. Sampling took place every second day over a period of 50 days, and all variables were taken with an integrated water sampler (HydroBios, IWS) pre-programed to fill from 0 – 10 m depth and all samples consisted of this integrated samples from the upper 10 m. The samples were stored dark in cool boxes and brought back to the laboratory and processed right away. Sampling took place in the morning, and the samples were usually back in the laboratory around noon. Measured variables included inorganic nutrients, dissolved organic nutrients, extracellular enzyme activity: leucine aminopeptidase (LAP) and alkaline phosphatase activity (APA), and the phytoplankton and bacterial community composition.

Description: The cruise Sternfahrt_8 was a continuation of the previous Sternfahrten (1-7). This time the aim was to assess not only the spatial variability but also the temporal variance of chemical, physical and greenhouse gases in the German Bight (North Sea). Therefore, three ships with different tracks repeated the same track with the same stations for four days (GPS-Positions see metadata). One Ship (Uthörn) covered the western part of our study area, the second ship (Littorina) covered the northern part (Büsum – Heligoland) and the third ship (Ludwig Prandtl) was supposed to take the middle part (Cuxhaven – Heligoland), but due to vandalism damage in the beginning of the cruise this ship was not able to participate in the cruise. Apart from continuously measurements six CTD stations were run each day delivering discrete water samples for DIC, TA, DOC, methane, nutrients and explosive metals. This dataset contains the results from the latter water samples. For more detailed information about the MOSEShx campaign and the cruise Sternfahrt_8 respectively see article cited in references.

Description: Oxygen minimum zones (OMZs) in the ocean are characterized by enhanced carbon dioxide (CO2) levels and are being further acidified by increasing anthropogenic atmospheric CO2. To investigate how on-going ocean deoxygenation will impact biogeochemical processes, a large-scale mesocosm experiment was conducted offshore Peru in austral summer (Feb-Apr) 2017, coinciding with a rare coastal El Niño event. We deployed eight mesocosms, each with a volume of 55 m3 and a length of 19 m, at the surface water in the coastal area of Callao (12.06° S, 77.23° W). The mesocosm bags were filled by surrounding surface water with daily or every-2nd-day nutrient and CO2 measurements for 10 days to monitor the initial conditions. Deep water masses from two different locations in the nearby OMZs were collected (at a depth of 30 and 70 m, respectively) and added to the mesocosms to simulate upwelling events on day 13 (see Bach et al., 2020 for details). Here we report every-2nd-day measurements of carbonate chemistry parameters in the individual mesocosms and the surrounding Pacific waters over 50 days. Depth-integrated seawater samples were taken from the surface (0-10 m for day 3-28; 0-12.5 m for day 29-50) and bottom layer (10-17 m for day 3-28; 12.5-17 m for day 29-50) of the mesocosms and the surrounding coastal water (named “Pacific”) using a 5-L integrating water sampler. Total alkalinity (TA) was measured by a two-stage open-cell potentiometric titration using a Metrohm 862 Compact Titrosampler, Aquatrode Plus (Pt1000) and a 907 Titrando unit, and pH (total scale) was measured spectrophotometrically by measuring the absorbance ratios after adding the indicator dye m-cresol purple (mCP) on a Varian-Cary 100 double-beam spectrophotometer (Varian). With inputs of the measured TA and pH, other CO2 parameters, such as dissolved inorganic carbon, pCO2, calcite and aragonite saturation state, and CO2 fluxes (FCO2), were calculated using the Excel version of CO2SYS. The performance of pH and TA measurements were also evaluated by examining the standard deviations and range controls of triplicate measurements of samples or reference materials. Our observations showed an acidification of surface water in the mesocosms by the OMZ water addition, followed by a rapid drop in pCO2 to near or below the atmospheric level due to enhance phytoplankton production. The positive CO2 fluxes in the surrounding Pacific waters indicated our study site was a local CO2 source during our study. Nevertheless, our mesocosm experiment suggests this CO2 export to the atmosphere can be largely dampened by biological processes. As a unique dataset that characterized near-shore carbonate chemistry with a high temporal resolution during a rare coastal El Niño event, our study gives important insights into the carbonate chemistry responses to extreme climate events in the Peruvian upwelling system.

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 mod- ify surface production and related biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predic- tions 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 con- trolling organic matter cycling in the coastal Peruvian up- welling 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 sub- surface waters at two different locations in the regional oxy- gen minimum zone (OMZ) and injected these into four meso- cosms (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 indi- vidual mesocosms. The mesocosm phytoplankton commu- nities were initially dominated by diatoms but shifted to- wards a pronounced dominance of the mixotrophic dinoflag- ellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift coincided with a short-term increase in production during the A. san- guinea 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 decou- pled from surface production and sustained by the remain- ing 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 limita- tion which constrained phytoplankton growth. Thus, gain and loss processes remained balanced and there were few oppor- tunities for blooms, which represents an event where the sys- tem becomes unbalanced. Overall, our mesocosm study re- vealed some key links between ecological and biogeochem- ical processes for one of the most economically important regions in the oceans.

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.