Limnology and Oceanography最新文献

Many aquatic primary producers can use bicarbonates as a carbon source for photosynthesis. Charophytes of the two genera: Chara and Nitellopsis are quite efficient in this process. Some species of these macroalgae produce carbonate encrustations, mainly calcium carbonate, constituting up to 86% of the summer maximum dry weight of the standing crop. In this study, we analyzed the fate of inorganic carbon accumulated this way in Chara spp. and Nitellopsis obtusa from six Polish lakes located in two regions (warmer W Poland and cooler NE Poland). Our study distinguished two groups of charophyte species that differed in the way of CaCO₃ release from their summer standing crops. On average, the corticate Chara rudis and C. tomentosa belonging to the first group were less efficient in depositing CaCO₃ from summer to autumn than the less corticate C. contraria and ecorticate N. obtusa of the second group. The latter two species were more efficient in inorganic carbon burial in sediments. On the contrary, dissolution of encrustation was more typical of the first species group and was facilitated by decreasing the pH and saturation index of calcite in lake water. The final output of CaCO₃ loss mainly resulted from combined species-specific features, lake water properties and overwintering patterns. Our study revealed that inorganic carbon cycling through charophytes involves burial and dissolution and is more complex than previously thought.

The ocean carbonate system is critical to monitor because it plays a major role in regulating Earth's climate and marine ecosystems. It is monitored using a variety of measurements, and it is commonly understood that all components of seawater carbonate chemistry can be calculated when at least two carbonate system variables are measured. However, several recent studies have highlighted systematic discrepancies between calculated and directly measured carbonate chemistry variables and these discrepancies have large implications for efforts to measure and quantify the changing ocean carbon cycle. Given this, the Ocean Carbonate System Intercomparison Forum (OCSIF) was formed as a working group through the Ocean Carbon and Biogeochemistry program to coordinate and recommend research to quantify and/or reduce uncertainties and disagreements in measurable seawater carbonate system measurements and calculations, identify unknown or overlooked sources of these uncertainties, and provide recommendations for making progress on community efforts despite these uncertainties. With this paper we aim to (1) summarize recent progress toward quantifying and reducing carbonate system uncertainties; (2) advocate for research to further reduce and better quantify carbonate system measurement uncertainties; (3) present a small amount of new data, metadata, and analysis related to uncertainties in carbonate system measurements; and (4) restate and explain the rationales behind several OCSIF recommendations. We focus on open ocean carbonate chemistry, and caution that the considerations we discuss become further complicated in coastal, estuarine, and sedimentary environments.

This study quantified the seasonal and spatial variability of partial pressure of CO₂ (pCO₂) and water-atmosphere CO₂ fluxes in the Parnaíba River Delta, the largest delta in the Americas. It is a pristine equatorial, mangrove-dominated environment located in a transitional between humid and semi-arid climates, with marked seasonality in rainfall and river discharge. Major channels and bays were sampled during dry and wet seasons, with continuous measurements of pCO₂, temperature, salinity, and wind velocity. Subsurface water samples were collected in discrete stations for pH, total alkalinity (TA), dissolved inorganic carbon (DIC), dissolved oxygen and chlorophyll a quantification. A significant positive correlation between carbonate system parameters with salinity was found in both periods, with salinity significantly higher in the dry season. Strong deviations of pCO₂, TA, and DIC from two endmembers conservative mixing were found, particularly in mangrove-dominated waters, due to organic matter degradation. The Delta showed high spatial variability of pCO₂, with the highest values in mangrove-dominated waters, moderate in the river-dominated regions, and lowest in the high salinity areas, suggesting that pCO₂ variability is likely controlled by a combination of river-ocean mixing and biological processes (respiration and photosynthesis). The Delta outgasses about 20 times less CO₂ in the dry season (9.06 ± 11.09 mmol m⁻².d⁻¹) than in the rainy season (209.68 ± 250.87 mmol m⁻² d⁻¹). Our results indicate this large mangrove-dominated tropical delta is an important source of CO₂ to the atmosphere, but a sharp decrease was observed during dry periods.

Long-lived crustose coralline algae are important ecosystem engineers and environmental archives in regions where observations of climate variability are sparse. Clathromorphum compactum is a cold-water alga that precipitates calcite that serve as archives of change at annual to sub-annual resolution. Understanding how environmental variability impacts the growth of this species is imperative for application in paleoclimate research, and for evaluating its vulnerability to change. Here, we present the results of the first, to-our-knowledge, controlled laboratory experiment isolating the effects of light, temperature, and salinity on calcification rates of C. compactum. Algal calcification rates were modulated by a combination of light exposure, salinity, and temperature, where temperature and salinity were positively correlated, and light level was negatively correlated with calcification rate. Linear extension of the skeleton also varied with treatment conditions, with the epithallial and perithallial layers of skeleton responding differently. Epithallial extension increased with salinity, while perithallial extension was governed only by a positive parabolic relationship with temperature. These results suggest that C. compactum growth will be impacted by environmental changes predicted for the Arctic over the coming decades. While increased temperature in the region may facilitate calcification in the algae, reductions in salinity associated with increased sea ice melt, and potentially increased light levels, may counteract this effect. The negative impact of increased light levels on algal calcification observed may not reflect the true impact of light availability on growth associated with a lengthening of the growing season (not evaluated in this study) accompanying reductions in annual sea-ice.

The melting cryosphere adds heterogeneity to the abiotic and biotic characteristics of many high latitude and montane rivers. However, climate change threatens the cryosphere's persistence in many regions. While existing research has explored the impacts of cryospheric loss on the diversity and structure of freshwater communities, implications for functional traits of communities, such as production of aquatic invertebrates, remain unresolved. Here, we quantified aquatic invertebrate community structure and secondary production in southeast Alaska (USA) streams that represent a meltwater to non-meltwater gradient, including streams fed primarily by: (1) glacier-melt, (2) snowmelt, (3) rainfall, and (4) a combination of these sources. We found alpha diversity was highest in the snow-fed stream and lowest in the glacier-fed stream. Annual secondary production was also lowest in the glacier-fed stream (0.56 g ash-free dry mass m⁻²), but 2–5 times higher in the other stream types primarily due to greater production of shared taxa that were found in all streams. However, despite low invertebrate diversity and productivity, the glacier-fed stream hosted distinct species assemblages associated with unique cycles of stream flow, water temperature, turbidity, and nutrient concentrations, which contributed to higher beta diversity between streams. Our findings suggest that the loss of glacier-melt contributions to rivers may result in increased freshwater invertebrate production but reduced beta diversity, which could have implications for community stability and the capacity of landscapes to support higher-level consumers, including fishes.

Most mesopelagic fish are small planktivores that migrate up at nightfall to feed in the safety of darkness and descend to depth at dawn to escape visual predators. However, the trophic roles can reverse since mesopelagic fishes also predate eggs and larvae of their predators. We use the Atlantic bluefin tuna as a model species to test the hypothesis that fishes in the open ocean synchronize spawning to moon-lit nights (when mesopelagic fishes avoid near-surface waters) to increase offspring fitness. Our analysis over two decades of field observations shows that tuna spawn most intensively the week before full moon. This fits predictions from a mechanistic model where spawning around full moon increases offspring fitness by two orders of magnitude due to low predation from mesopelagic fishes. Circalunar patterns of food availability can also favor fitness of offspring spawned the days before full moon. Our findings suggest that mesopelagic fishes may have an important impact on pelagic fish through predation of early life stages and cause an evolutionary drive to synchronize spawning to the lunar cycle.