Replication and Treatment Strength in Whole‐Lake Experiments

Recent changes in atmospheric input and primary productivity in the north Indian Ocean

Abstract. Ocean deoxygenation is a rising threat to marine ecosystems and food resources under present climate warming conditions. Organic-rich sapropel layers deposited in the Mediterranean Sea provide a natural laboratory to study the processes that have controlled changes in seawater oxygen levels in the recent geological past. Our study is based on three sediment cores spanning the last 10 000 years and located on a bathymetric transect offshore from the western distributaries of the Nile delta. These cores are partly to continuously laminated in the sections recording sapropel S1, which is indicative of bottom-water anoxia above the western Nile deep-sea fan. We used a combination of microfacies analyses and inorganic and organic geochemical measurements to reconstruct changes in oxygenation conditions at seasonal to millennial timescales. Millimetre-thick laminations are composed of detrital, biogenic and chemogenic sublayers reflecting seasonal successions of sedimentation. Dark layers reflect the deposition of summer floods and two types of light layers correspond to autumn plankton blooms and authigenic carbonates formed in the water column during spring–early summer, respectively. The isotopic signature of the authigenic carbonates suggests permanent anoxic to euxinic bottom waters resulting in high levels of anaerobic remineralization of organic matter and highlights their potential to reconstruct seawater chemistry at times when benthic fauna was absent. Ratios of major elements combined with biomarkers of terrestrial and marine organic matter and redox-sensitive compounds allow changes in terrigenous input, primary productivity and past deoxygenation dynamics on millennial timescales to be tracked. Rapid fluctuations of oxygenation conditions in the upper 700 m water depth occurred above the Nile deep-sea fan between 10 and 6.5 ka BP, while deeper cores recorded more stable anoxic conditions. Synchronous changes in terrigenous input, primary productivity and past oxygenation dynamics after 6.5 ka BP show that runoff-driven eutrophication played a central role in rapid oxygenation changes in the south-eastern Levantine Basin. These findings are further supported by other regional records and reveal time-transgressive changes in oxygenation state driven by rapid changes in primary productivity during a period of long-term deep-water stagnation.

Vertebrate populations throughout the circumpolar north often exhibit cyclic dynamics, and predation is generally considered to be a primary driver of these cycles in a variety of herbivore species. However, weather and climate play a role in entraining cycles over broad landscapes and may alter cyclic dynamics, although the mechanism by which these processes operate is uncertain. Experimental and observational work has suggested that weather influences primary productivity over multi-year time periods, suggesting a pathway through which weather and climate may influence cyclic herbivore dynamics. Using long-term monitoring data, we investigated the relationships among multi-year weather conditions, measures of primary productivity, and the abundance of two cyclic herbivore species: snowshoe hare and northern red-backed vole. We found that precipitation (rain and snow) and growing season temperatures were strongly associated with variation in primary productivity over multi-year time horizons. In turn, fourfold variation in the amplitude of both the hare and vole cycles observed in our study area corresponded to long-term changes in primary productivity. The congruence of our results for these two species suggests a general mechanism by which weather and climate might influence cyclic herbivore population dynamics. Our findings also suggested that the association between climate warming and the disappearance of cycles might be initiated by changes in primary productivity. This work provides an explanation for observed influences of weather and climate on primary productivity and population cycles and will help our collective understanding of how future climate warming may influence these ecological phenomena in the future.

Tight benthic-pelagic coupling drives seasonal and interannual changes in iron‑sulfur cycling in Arctic fjord sediments (Kongsfjorden, Svalbard)

Sedimentary record of primary productivity changes in a crater lake in Northeast China since the Last Glacial Maximum

Short sediment cores (80–100 cm) from three Florida (USA) lakes (Sheelar, Wauberg, and Apopka) that range in trophic status, were analyzed for total organic carbon (TOC), total nitrogen, stable isotopes of organic carbon (δ13CTOC) and biomarkers (n-alkanes and fatty acids), to identify the sources of organic matter in the lake deposits, and to link changes in primary productivity to anthropogenic activities during the last ~ 150 years. Relatively small (0.07 km2), ultra-oligotrophic Lake Sheelar is located in a state park, and sediment analyses indicate stable trophic status in the water body since at least the middle of the nineteenth century. Algal biomarkers are in low abundance throughout the core and terrestrial lipids and δ13CTOC values suggest that vascular plants were the primary source of TOC to the lake sediments during the period of record. In larger, eutrophic Lakes Wauberg (1.5 km2) and Apopka (125 km2), algal-derived biomarkers increase in recent sediments, whereas δ13CTOC values and concentrations of terrestrial biomarkers decrease toward the sediment surface. Increasing dominance through time of autochthonous carbon sources in the Lake Wauberg and Apopka sediment records coincides with specific anthropogenic activities in the respective watersheds. Submersed macrophytes in Lake Wauberg were replaced by algal communities in the mid-1980s, following expansion of residential development in the watershed. Biomarker data from the Lake Apopka core show there was an abrupt transition in the lake in the late 1940s, from domination by vascular plants to domination by algae, which has been documented by other paleolimnological studies that used alternative trophic state indicators. The trophic state shift in Lake Apopka corresponds to a period of increased nutrient input to the lake, associated with extensive farming along the north shore. Florida lakes have experienced different trophic state trajectories over the last ~ 150 years, driven by specific human activities in their respective watersheds.

The hypothesis that the importance of dissolved organic matter (DOM) as a reservoir of C, N, and P declines, relative to that of the particulate pool, with increasing nutrient inputs was tested using mesocosms exposed to a gradient of nutrient inputs in the Spanish Mediterranean. The nutrient additions included a treatment equivalent to the loading in the coastal ecosystem studied (5 mmol N m−2 d−1), and mesocosms receiving half , 2-, 4-, 8-, and 16-fold this value, as well as a mesocosm to which no nutrients were added. Nutrients were added at ratios of 20 N (as ammonium) : 7 Si : 1 P. The initial concentration of dissolved inorganic nutrients was very low (dissolved inorganic nitrogen 75%). Particulate and dissolved organic matter was depleted in N (C/N ratio > 15) and, particularly, P (C/P ratio > 1000), indicative of a strongly nutrient, particularly phosphorus, deficient ecosystem. Experimental nutrient additions lead to a parabolic change in C/N and C/P ratios in the dissolved organic matter with increasing nutrient inputs, which approached the Redfield stoichiometry at nutrient inputs > 8 fold above the ambient loading. The relative size of the dissolved inorganic nutrient pools (about 20% of the N and P) did not vary, but there was a tendency towards an increase in the relative size of the particulate pool at the expense of a decrease in the relative importance of DOM as a reservoir of N, P and C, with increasing nutrient inputs. The production of nutrient-depleted organic matter at low nutrient inputs likely prevents efficient recycling, leading to the dominance of nutrients in DOM in the system.

Adaptive beamforming techniques are widely used in radar, communication, sonar, navigation and other signal processing fields. The conventional experimental systems for adaptive beamforming are often carried out with a large number of Radio Frequency equipment, which leads to high cost and complexity. Therefore, it is necessary to construct an experimental system with low cost and high flexibility to verify the performance of adaptive beamforming algorithms. In this paper, an experimental adaptive beamforming platform by utilizing the microphone array is designed, where the principle of adaptive beamforming, the structure and function of each part of whole experiment system are introduced clearly. Furthermore, the corresponding experiments are deployed to verify the adaptive beamforming algorithms for radar system. The experimental results show that the designed experimental platform can validate the adaptive beamforming algorithms easily and effectively. (5 pages)

Nutrient inputs from the atmosphere and rivers to the ocean are increased substantially by human activities. These increasing inputs of nutrients from human activities promote oceanic NPP, potentially partially counteracting decreases caused by climate change. Then, increases in export of organic matter to the ocean interior and its decomposition consumes dissolved oxygen. Therefore, nutrient inputs to the ocean promote carbon uptake and amplify climate-driven ocean deoxygenation. However, the previous generation of Earth system models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5), which contributed substantially to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, did not account for anthropogenic nutrient inputs to the ocean. Several CMIP phase 6 (CMIP6) Earth system models do consider anthropogenic nutrient inputs to the ocean for the historical period, but their impact on ocean biogeochemical cycles has not been fully assessed, even for individual Earth system models. Therefore, our understanding of the impact of such perturbations on ocean biogeochemistry is even less complete than that associated with climate change. In particular, the quantitative relationship between the effects of climate change on ocean biogeochemical cycles and those of anthropogenic nutrient inputs remains poorly understood.In this study, using historical simulations by one of the CMIP6 models (MIROC-ES2L) that considers anthropogenic nutrient inputs, we demonstrate that the contribution of anthropogenic nutrient inputs to past changes in global oceanic productivity, carbon uptake, and deoxygenation is of similar magnitude to the effect of climate change. In particular, two noteworthy results are obtained: (1) that anthropogenic fertilization could more than counteract the expected decrease in NPP caused by ocean warming and stratification for the historical period, and (2) that it could accelerate climate-driven deoxygenation in the upper ocean, helping to close the gap between models and observations. Additionally, current estimation of the imbalance in the carbon budget could be explained partially by increase in oceanic carbon uptake associated with anthropogenic nutrient inputs to the ocean. These improvements provide support regarding the significant contribution of anthropogenic nutrient inputs to global changes in ocean biogeochemistry. Considering the effects of both nutrient inputs and climate change is crucial in assessing anthropogenic impacts on ocean biogeochemistry.

The Mediterranean Sea is considered as a hotspot for climate change because of its location in the temperate region and because it is a semi-enclosed basin surrounded by highly populated and developed countries. Some expected changes include an increase in air temperature and changes in the periodicity and spatial distribution of rainfall. Alongside, demographic and politics changes will alter freshwater quantity and quality. All these changes will have an impact on the ecological status of marine ecosystems in the basin. We use a 3D hydrodynamic-biogeochemical coupled model of the entire Mediterranean Sea to explore potential changes in primary productivity (mean values and spatial distribution) under two emission scenarios (rcp4.5 and rcp8.5).To isolate the effects of changes in atmospheric conditions alone, in this ensemble of simulations rivers conditions (water flow and nutrient concentrations) are kept unchanged and equal to its climatological values for the last 10 years. Despite the significant warming trend, the mean integrated primary production rate in the entire basin remains almost unchanged. However characteristic spatial differences are consistently found in the different simulations. The western basin becomes more oligotrophic associated to a surface density decrease (increase stratification) because of the influence of the Atlantic waters which prevents surface salinity to increase. In the eastern basin, on the contrary, all model runs simulates an increase in surface production linked to a density increase (less stratification) because of the increasing evaporation rate. The simulations presented here demonstrate the basic response patterns of the Mediterranean Sea ecosystem to changing climatological conditions. Although unlikely, they could be considered as a ‘baseline’ of expected consequences of climatic changes on marine conditions in the Mediterranean.

The response of deep-water benthic foraminiferal assemblages to changes in paleoproductivity during the Pleistocene (last 769.2 kyr), western South Atlantic Ocean

A multi-proxy paleolimnological analysis of a sediment core sequence from Lake Malaya Chabyda in Central Yakutia (Eastern Siberia, Russia) was conducted to investigate changes in lake processes, including lake development, sediment and organic carbon accumulation, and changes in primary productivity, within the context of Late Pleistocene and Holocene climate change. Age-depth modeling with 14C indicates that the maximum age of the sediment core is ∼14 cal kBP. Three distinct sedimentary units were identified within the sediment core. Sedimentological and biogeochemical properties in the deepest section of the core (663–584 cm; 14.1–12.3 cal kBP) suggests a lake environment mostly influenced by terrestrial vegetation, where organic carbon accumulation might have been relatively low (average ∼100 g OC m−2 a−1), although much higher than the global modern average. The middle section of the core (584–376 cm; 12.3–9.0 cal kBP) is characterized by higher primary productivity in the lake, much higher sedimentation, and a remarkable increase in OC delivery (average ∼300 g OC m−2 a−1). Conditions in the upper section of the core (<376 cm; < 9.0 cal kBP) suggest high primary productivity in the lake and high OC accumulation rates (average ∼200 g OC m−2 a−1), with stable environmental conditions. The transition from organic-poor and mostly terrestrial vegetation inputs (TOC/TNatomic ratios ∼20) to conditions dominated by aquatic primary productivity (TOC/TNatomic ratios <15) occurs at around 12.3 cal kBP. This resulted in an increase in the sedimentation rate of OC within the lake, illustrated by higher sedimentation rates and very high total OC concentrations (>30%) measured in the upper section of the core. Compact lake morphology and high sedimentation rates likely resulted in this lake acting as a significant OC sink since the Pleistocene-Holocene transition. Sediment accumulation rates declined after ∼8 cal k BP, however total OC concentrations were still notably high. TOC/TNatomic and isotopic data (δ13C) confirm the transition from terrestrial-influenced to aquatic-dominated conditions during the Early Holocene. Since the mid-Holocene, there was likely higher photosynthetic uptake of CO2 by algae, as suggested by heavier (isotopically enriched) δ13C values (>−25‰).

The objective of this paper is to evaluate the adaptability of different water control completion techniques in offshore horizontal wells under varying reservoir conditions. The scope includes integrating large-scale physical experiments with numerical modeling to analyze the performance of distinct ICD/AICD valves across different fluid viscosities and flow rates. Existing studies often focus on numerical simulations or single-valve flow testing. To address this limitation, this research employed an integrated experimental-numerical approach. A large-scale experiment system was designed and built to test multiple ICD/AICD valves simultaneously under controlled conditions. The experiment system incorporated actual reservoir parameters, completion configurations, and fluid properties. The study quantified water breakthrough time, the change of water cut over time, and oil-water rate of production fluid across different flow rates and fluid viscosities. Numerical simulations with controlled variables were used to validate results and extend the analysis for more combinations of reservoir conditions and production parameters. Experimental results demonstrate distinct adaptability profiles for each device. At low viscosity (4 cP): The 4 mm Floating-disc AICD exhibited superior sensitivity, extending the water-free production period significantly due to the disc structure. At high viscosity (130 cP): The 2 mm Channel-type AICD outperformed other designs. Its fixed flow path provided stable flow resistance, effectively delaying water breakthrough and maintaining a lower water cut under high-viscosity conditions where the floating-disc mechanism became less responsive. At higher production rates (30 m3/d), flow turbulence increased; however, the 2 mm Channel-type AICD maintained the most consistent water control performance across all tested viscosities. This study provides critical experimental data quantifying the water control effect for different AICD mechanisms. The findings offer a practical selection criterion for field engineers: prioritizing Floating-disc AICDs for light oil reservoirs and Channel-type AICDs for heavy oil applications to maximize water control effectiveness.

A centennial scale organic-walled dinoflagellate cyst record of the last deglaciation in the South Adriatic Sea (Central Mediterranean)

The distribution characteristics and formation of marine anoxic conditions through the Late Ordovician–Early Silurian (O–S) remain poorly resolved despite their importance in the preservation of sedimentary organic matter and the formation of black shale. In this study, the major, trace, and pyrite δ34S (δ34Spy) contents of 36 shale samples at the edge of the southwest depocenter of the Upper Yangtze Basin (Tianlin and Changhebian sections) were analyzed to understand the redox conditions, terrigenous clastic inputs, and primary productivity changes. The iron speciation and enrichment factor of U and Mo show that the range of anoxic conditions gradually expanded from the sedimentation center to the edge during the late Katian stage, peaked in the early Hirnantian stage followed by a rapid decrease, and expanded again during the early Rhuddanian stage. Comprehensive index analysis showed that the increase of terrigenous clastic input and the relative decrease of primary productivity due to tectonism and sea level change controlled the transformation of the water column from anoxic, especially euxinic, to suboxic-oxic conditions. This is reflected in the correlation between paleo-salinity, δ34Spy, chemical index of alteration, and the organic carbon accumulation rate. This work emphasizes the control of terrigenous clastic input and sulfate availability on the transformation of marine redox conditions during the O-S period in semi-restricted basins.