Description: A Lagrangian analysis of particles sinking through a velocity field observed by Eulerian frame measurements was used to evaluate the effects of horizontal advection and particle sinking speed on particle fluxes as measured by moored sediment traps. Characteristics of the statistical funnel above moored deep-ocean sediment traps at the German JGOFS quasi-time series station at 47N, 20W (Biotrans site) were determined. The analysis suggests that the distance and direction between a given sediment trap and the region at the surface where the particles were produced depends on the mean sinking velocity of the particles, the horizontal velocity field above the trap and the deployment depth of the trap. Traps moored at different depths at a given mooring site can collect particles originating from different, separated regions at the surface ocean. Catchment areas for a given trap vary between different years. Typical distances between catchment areas of traps from different water depth but for a given time period (e.g., the spring season) are similar or even larger compared to typical length scales of mesoscale variability of phytoplankton biomass observed in the temperate northeast Atlantic. This implies that particles sampled at a certain time at different depth horizons may originate from completely independent epipelagic systems. Furthermore catchment areas move with time according to changes in the horizontal flow field which jeopardizes the common treatment of interpreting a series of particle flux measurements as a simple time series. The results presented in this work demonstrate that the knowledge of the temporal and spatial variability of the velocity field above deep-ocean sediment traps is of great importance to the interpretation of particle flux measurements. Therefore, the one-dimensional interpretation of particle flux observations should be taken with care.

Description: In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems resulting from the EU-FP7 project HYPOX (“In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies”, www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences. Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxygenation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of watercolumn oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were resolved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the microbially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts.

Description: We present our experiences in monitoring hypoxia and assessing oxygen-related phenomena in aquatic systems, resulting from the EU-FP7 project HYPOX (“In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and land-locked water bodies”, www.hypox.net). For this presentation, we selected approaches and technologies which could be relevant for monitoring fast fluctuations at the pelagic redoxcline, seasonal benthic hypoxia and decadal trends oxycline boundary shifts in the Black Sea. Using novel technologies like e.g., the profiling instrumentation platform GODESS, ARGO floats with oxygen optodes and long-term moorings equipped with ADCP and oxygen optodes, temporal and spatial patterns of water column oxygenation from hours to seasons, and from basin-scale to local-scale patterns were resolved. We present examples from study sites in the Baltic Sea and in the Black Sea. The time series recordings of GODESS and mooring arrays allowed a thorough characterization of oscillating redoxclines in the central Baltic Sea and in the Black Sea off southwestern Crimea as temporally dynamic, three-dimensional systems. For the first time, oxygen sensor equipped ARGO type profiling floats were deployed in the Black Sea and proved to be powerful tools to address seasonal changes in patterns of water column oxygenation on larger spatial scales and emphasize the importance of mesoscale processes for oxygen distribution in the Black Sea basin. A 3-month continuous time series recording of a stand-alone static mooring equipped with optical oxygen sensors, current meters, and turbidity sensors identified summer hypoxia to be a highly dynamic process and provided insights into the controls of hypoxia formation on the north-western Black Sea shelf. Existing multi-decadal time-series monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions and, hence, the importance of maintaining long-term commitments to oxygen monitoring programs. Such time series data allow separating out the effects that climatic forcing and eutrophication exert on oxygen depletion i.e., in the Black Sea. Standard CTD measurements in the central Black Sea over the last 90 years reflect the rising of the upper boundary of the suboxic zone in the 1970s and 1980s due to eutrophication, and again in the 1990s and 2000s due to NAO forcing, while eutrophication relaxed. Our comprehensive study within HYPOX was able to address many aspects of hypoxia in aquatic systems and revealed the vital need for dedicated oxygen monitoring at appropriate spatial and temporal scales with appropriate technologies. The variety of hypoxia characteristics and consequences emphasizes also the need for a careful selection of locations and periods of time for oxygen observations in order to adequately address the risk for hypoxia formation and ecosystem response.

Description: This dataset provides 37 CTD profiles measured on board of the German R/V Sonne (cruise SO269) in the northern South China Sea, under the project SOCLIS – South China Sea Natural Laboratory under Climatic and Anthropogenic Stress, in August and September 2019. The 37 profiles of temperature, salinity, dissolved oxygen, fluorescence, turbidity, surface irradiance (SPAR) and Photosynthetically active radiation (PAR), and sound velocity were measured using a CTD Sea-Bird SBE 911 plus, together with oxygen sensor (SBE 43), PAR sensor (Biospherical, QCP-2350 + QSR-2200), and a fluorometer (WET Labs ECO-FLNTU(RT)D). Additionally, dissolved oxygen, potential temperature and sigma-theta (with reference to the surface) were calculated. The 37 additional CTD files complement the physical oceanography dataset (Waniek et al., 2021).

Description: This dataset provides 131 CTD profiles measured on board of the German R/V Sonne (cruise SO269) in the northern South China Sea, under the project SOCLIS – South China Sea Natural Laboratory under Climatic and Anthropogenic Stress, in August and September 2019. The 131 profiles of temperature, salinity, dissolved oxygen, fluorescence, turbidity, surface irradiance (SPAR) and Photosynthetically active radiation (PAR), and sound velocity were measured using a CTD Sea-Bird SBE 911 plus, together with oxygen sensor (SBE 43), PAR sensor (Biospherical, QCP-2350 + QSR-2200), and a fluorometer (WET Labs ECO-FLNTU(RT)D). Additionally, oxygen saturation, potential temperature and sigma-theta (with reference to the surface) were calculated. The 131 CTD profiles are distributed by 81 stations and aim to study the impact of a growing anthropogenic pressure around the Pearl River Estuary into the northern shelf of the South China Sea towards the deep sea. The dataset was used to study the presence and spatial distribution of natural and synthetic estrogenic compounds and pharmaceutical and personal care products (PPCPs) in the Pearl River Estuary and northern shelf of the South China Sea.

Description: This dataset provides 131 CTD profiles measured on board of the German R/V Sonne (cruise SO269) in the northern South China Sea, under the project SOCLIS – South China Sea Natural Laboratory under Climatic and Anthropogenic Stress, in August and September 2019. The 131 profiles of temperature, salinity, dissolved oxygen, fluorescence, turbidity, surface irradiance (SPAR) and Photosynthetically active radiation (PAR), and sound velocity were measured using a CTD Sea-Bird SBE 911 plus, together with oxygen sensor (SBE 43), PAR sensor (Biospherical, QCP-2350 + QSR-2200), and a fluorometer (WET Labs ECO-FLNTU(RT)D). Additionally, oxygen saturation, potential temperature and sigma-theta (with reference to the surface) were calculated. The 131 CTD profiles are distributed by 81 stations and aim to study the impact of a growing anthropogenic pressure around the Pearl River Estuary into the northern shelf of the South China Sea towards the deep sea. The dataset was used to study the presence and spatial distribution of natural and synthetic estrogenic compounds and pharmaceutical and personal care products (PPCPs) in the Pearl River Estuary and northern shelf of the South China Sea.

Description: This dataset provides 131 CTD profiles measured on board of the German R/V Sonne (cruise SO269) in the northern South China Sea, under the project SOCLIS – South China Sea Natural Laboratory under Climatic and Anthropogenic Stress, in August and September 2019. The 131 profiles of temperature, salinity, dissolved oxygen, fluorescence, turbidity, surface irradiance (SPAR) and Photosynthetically active radiation (PAR), and sound velocity were measured using a CTD Sea-Bird SBE 911 plus, together with oxygen sensor (SBE 43), PAR sensor (Biospherical, QCP-2350 + QSR-2200), and a fluorometer (WET Labs ECO-FLNTU(RT)D). Additionally, oxygen saturation, potential temperature and sigma-theta (with reference to the surface) were calculated. The 131 CTD profiles are distributed by 81 stations and aim to study the impact of a growing anthropogenic pressure around the Pearl River Estuary into the northern shelf of the South China Sea towards the deep sea. The dataset was used to study the presence and spatial distribution of natural and synthetic estrogenic compounds and pharmaceutical and personal care products (PPCPs) in the Pearl River Estuary and northern shelf of the South China Sea.

Description: This dataset provides 131 CTD profiles measured on board of the German R/V Sonne (cruise SO269) in the northern South China Sea, under the project SOCLIS – South China Sea Natural Laboratory under Climatic and Anthropogenic Stress, in August and September 2019. The 131 profiles of temperature, salinity, dissolved oxygen, fluorescence, turbidity, surface irradiance (SPAR) and Photosynthetically active radiation (PAR), and sound velocity were measured using a CTD Sea-Bird SBE 911 plus, together with oxygen sensor (SBE 43), PAR sensor (Biospherical, QCP-2350 + QSR-2200), and a fluorometer (WET Labs ECO-FLNTU(RT)D). Additionally, oxygen saturation, potential temperature and sigma-theta (with reference to the surface) were calculated. The 131 CTD profiles are distributed by 81 stations and aim to study the impact of a growing anthropogenic pressure around the Pearl River Estuary into the northern shelf of the South China Sea towards the deep sea. The dataset was used to study the presence and spatial distribution of natural and synthetic estrogenic compounds and pharmaceutical and personal care products (PPCPs) in the Pearl River Estuary and northern shelf of the South China Sea.