Climate variability shifts the vertical structure of phytoplankton in the Sargasso Sea

Abstract. Earth system models suggest that anthropogenic climate change will influence marine phytoplankton over the coming century with light-limited regions becoming more productive and nutrient-limited regions less productive. Anthropogenic climate change can influence not only the mean state but also the internal variability around the mean state, yet little is known about how internal variability in marine phytoplankton will change with time. Here, we quantify the influence of anthropogenic climate change on internal variability in marine phytoplankton biomass from 1920 to 2100 using the Community Earth System Model 1 Large Ensemble (CESM1-LE). We find a significant decrease in the internal variability of global phytoplankton carbon biomass under a high emission (RCP8.5) scenario and heterogeneous regional trends. Decreasing internal variability in biomass is most apparent in the subpolar North Atlantic and North Pacific. In these high-latitude regions, bottom-up controls (e.g., nutrient supply, temperature) influence changes in biomass internal variability. In the biogeochemically critical regions of the Southern Ocean and the equatorial Pacific, bottom-up controls (e.g., light, nutrients) and top-down controls (e.g., grazer biomass) affect changes in phytoplankton carbon internal variability, respectively. Our results suggest that climate mitigation and adaptation efforts that account for marine phytoplankton changes (e.g., fisheries, marine carbon cycling) should also consider changes in phytoplankton internal variability driven by anthropogenic warming, particularly on regional scales.

The climate of the western shelf of the Antarctic Peninsula (WAP) is undergoing a transition from a cold-dry polar-type climate to a warm-humid sub-Antarctic-type climate. Using three decades of satellite and field data, we document that ocean biological productivity, inferred from chlorophyll a concentration (Chl a), has significantly changed along the WAP shelf. Summertime surface Chl a (summer integrated Chl a approximately 63% of annually integrated Chl a) declined by 12% along the WAP over the past 30 years, with the largest decreases equatorward of 63 degrees S and with substantial increases in Chl a occurring farther south. The latitudinal variation in Chl a trends reflects shifting patterns of ice cover, cloud formation, and windiness affecting water-column mixing. Regional changes in phytoplankton coincide with observed changes in krill (Euphausia superba) and penguin populations.

We analysed the changes in phytoplankton and in the main limnological features in a shallow lake during its transition from a clear-vegetated regime to a turbid one from 2005 to 2013. As samplings were discontinuous, data were analysed considering three different sampling periods. At the beginning of the first period, the lake was in a clear-vegetated regime, showing low values of chlorophyll a, KdPAR, total suspended solids and nutrients, and high Secchi depth. Phytoplankton was dominated by nano-phytoplanktonic species. During the second period, some evidences of the shift to a turbid regime were observed (mainly in KdPAR and total suspended solids). Towards the end of our study, submerged macrophytes sharply declined; in this period KdPAR and total suspended solids noticeably increased, whereas a significant reduction in Secchi depth occurred. Concomitantly, phytoplankton abundance augmented in two orders of magnitude, changing to a community with a higher proportion of micro-phytoplankton. Although the causes of the regimen shift could not be unequivocally assessed, the drastic reduction in the hydrometric level of the lake probably provoked a declination in macrophytes, with the consequent increase of nutrients in the water column and the increment in phytoplankton densities, carrying the system towards a turbid regime.

Marine phytoplankton have many obvious characters, such as rapid cell division rates and large population sizes, that give them the capacity to evolve in response to global change on timescales of weeks, months or decades. However, few studies directly investigate if this adaptive potential is likely to be realized. Because of this, evidence of to whether and how marine phytoplankton may evolve in response to global change is sparse. Here, we review studies that help predict evolutionary responses to global change in marine phytoplankton. We find limited support from experimental evolution that some taxa of marine phytoplankton may adapt to ocean acidification, and strong indications from studies of variation and structure in natural populations that selection on standing genetic variation is likely. Furthermore, we highlight the large body of literature on plastic responses to ocean acidification available, and evolutionary theory that may be used to link plastic and evolutionary responses. Because of the taxonomic breadth spanned by marine phytoplankton, and the diversity of roles they fill in ocean ecosystems and biogeochemical cycles, we stress the necessity of treating taxa or functional groups individually.

Changes of Phytoplankton in East China Sea and Sea of Japan : Based on Satellite Data

Based on the materials from studies of phytoplankton in the SylvenskoChusovsky reach of the Kama Reservoir in July 2020 and 2022, its taxonomic composition, ecological-geographical structure and quantitative indicators were studied. The large marginal Sylvensko-Chusovsky reach of the Kama Reservoir is formed by the confluence of the Sylva and Chusovaya rivers and includes two districts and three sections (See Fig. 1). The mineralization of water throughout the reach varies significantly, from 225 to 1000 mgL-1, which is associated with the influx of river water. In the Sylva River, the average mineralization values in summer are significantly higher (650 mgL-1) than those of the Chusovaya River (250 mgL-1). Precipitation and surface inflow volumes in the study area (July 2020 and 2022) were below long-term averages. The years of research varied significantly in temperature regime: the water temperature of the Sylvensko-Chusovsky reach in 2020 was 30.3 ± 1.6°С, in 2022 – 20.3 ± 0.6°С. As a result of the study, 267 species and intraspecific taxa of algae from 9 departments were identified in the phytoplankton composition of the Sylvensko-Chusovsky reach of the Kama Reservoir. The basis of the species richness was formed by diatoms (36.0%), green (28.5%), golden (12.5%) algae, and cyanoprokaryotes (11.6%); the share of other algae departments totaled 11% (See Table 1). The species composition of phytoplankton differs in various parts of the reach, which is associated with the flow of river waters from the Sylva and Chusovaya rivers into the bays; the degree of floristic similarity according to the Sørensen-Chekanovsky coefficients is low and ranges from 0.41 to 0.68 (See Fig. 2). As a result of the carried-out work, the floristic list of algae of the Sylvensky Bay was replenished by 41%, previously numbering 69 species and varieties from 5 departments (See Fig. 3). In the ecological and geographical aspect, the algal flora of plankton is represented by typically planktonic species, widespread in water bodies of the globe, indifferent to water salinity, living only in fresh water bodies and preferring neutral waters (See Table 2). In Sylvensky Bay, the ecological structure of algocenoses retained its proportions from 2004 to 2022. During the summer low-water period of algal flora, the most significant contribution is made by cyanoprokaryotes, which appear with diatoms and green sea waves (See Fig. 4). Quantitative indicators of phytoplankton development varied significantly: abundance from 0.9 to 85.0 million cellsL-1, biomass from 0.39 to 13.02 mgL-1. Differences in the temperature regime during the years of the study determined the level of phytoplankton development; in 2022, the abundance and biomass values were three times higher compared to the abnormally hot 2020 (See Table 3). Throughout the entire water area, the dominant complex in number is represented mainly by species indicators of anthropogenic eutrophication (Aphanizomenon flos-aquaе, Aphanocapsa holsatica, Aulacoseira granulata, Stephanodiscus binderanus) and there is a massive development of non-heterocyst cyanoprokaryotes (Aphanocapsa holsatica, A. inserta, Anathece clathrata, Planktolyngbya limnetica, A. phanothece bachmannii). Dinophyte algae (Apocalathium aciculiferum, Peridinium cinctum, P. willei, Peridinium sp. and Gymnodinium sp.) played a significant role in the composition of dominant species by biomass, along with diatoms (See Table 4). As a result of the development of smallsized algal species, phytoplankton abundance values have increased more than 20-fold from 2004 to the present, while phytoplankton biomass has increased only twofold. The Shannon species diversity index values (2.96-5.02) indicate a complex structure and high biodiversity of phytoplankton. Higher index values were characteristic of riparian areas in 2022. Simpson's indices, reflecting the degree of expression of dominance of certain species, vary from 0.04 to 0.36 in the Sylvensko-Chusovsky Bay. The decrease of the index in the Chusovsky Bay (0.15 ± 0.03) is associated with a higher diversity of phytoplankton compared to the Sylvensky Bay (0.23 ± 0.05). Based on the composition of structure-forming species and the level of biomass, the trophic status of the Sylvensko-Chusovsky reach is determined as mesotrophic. Since the distribution of phytoplankton across the water area is uneven, the trophic state was assessed from β-oligotrophic in the Sylvensko-Chusovsky area to mesotrophic in the bays in 2020, and from mesotrophic to α-eutrophic level in 2022. The main changes in phytoplankton include a significant increase in the taxonomic diversity of golden algae, an increase in the coenotic role of disazotrophic cyanoprokaryotes and dinophyte algae, which indicates the progressive eutrophication of the waters of the Sylvensko-Chusovsky reach under the combined influence of anthropogenic factors and climate warming.

Climate variability and change, associated with increasing water demands, can have significant implications for water availability. In the Brazilian semi-arid, eutrophication in reservoirs raises the risk of water scarcity. The reservoirs have also a high seasonal and annual variability of water level and volume, which can have important effects on chlorophyll-a concentration (Chla). Assessing the influence of climate and hydrological variability on phytoplankton growth can be important to find strategies to achieve water security in tropical regions with similar problems. This study explores the potential of machine learning models to predict Chla in reservoirs and to understand their relationship with hydrological and climate variables. The model is based mainly on satellite data, which makes the methodology useful for data-scarce regions. Tree-based ensemble methods had the best performances among six machine learning methods and one parametric model. This performance can be considered satisfactory as classical empirical relationships between Chla and phosphorus may not hold for tropical reservoirs. Water volume and the mix-layer depth are inversely related to Chla, while mean surface temperature, water level, and surface solar radiation have direct relationships with Chla. These findings provide insights on how seasonal climate prediction and reservoir operation might influence water quality in regions supplied by superficial reservoirs.

Long-term changes in hydrochemistry and community structure of phytoplankton and macrophytes were analyzed in the Sestroretskiy Razliv reservoir (northwestern Russia). The average content of total phosphorus (TP) in May–October increased from 73 μg P l−1 in 1980 to 163 μg P l−1 in 2000. A significant increase in average chlorophyll a content from 16.6 μg l−1 in 1980 to 84.7 μg l−1 in 2000 and a shift in phytoplankton composition to the dominance of cyanobacteria over diatoms indicated a change in the trophic status of the reservoir from meso-eutrophic to hypertrophic. In 2016 and 2018, average TP was 96 and 101 μg P l−1, respectively. The average content of chlorophyll a was 43.6 μg l−1 in 2016 and 66.6 μg l−1 in warmer 2018, indicating persistent eutrophic conditions. Diatoms dominated both in 2016 and 2018, especially in 2016 characterized by unfavorable weather conditions. Cyanobacteria were more abundant in 2018 with higher summer temperatures. The decline of the total area covered by aquatic vegetation from 157 ha in 1980 to 76 ha in 2016 likely resulted from an increase in phytoplankton biomass and water turbidity. Based on the results of our observations, in addition to further reduction in nutrient loading, biomanipulation by introducing predatory fish as a restoration measure was proposed to improve the ecological status of the reservoir.

Satellite-derived estimates of primary production during the Sargasso Sea winter/spring bloom: Integration of in-situ time-series data and ocean color remote sensing observations

Atlantic Warm Pool (AWP) climate variability is subject to multiple influences of remote and local forcing. However, shortage of observational data before the midtwentieth century and of long‐term sea surface temperature (SST) and climate records has hampered the detection and investigation of decadal‐ and longer‐scale variability. We present new seasonally resolved 125‐year records of coral δ18O and Sr/Ca variations in the Central Caribbean Sea (Little Cayman, Cayman Islands; Diploria strigosa). Both geochemical proxies show decreasing long‐term trends, indicating long‐term warming. Sr/Ca indicates much stronger regional warming than large‐scale grid‐SST data, while δ18O tracks large‐scale SST changes in the Atlantic Warm Pool. Seawater δ18O variations are reconstructed, indicating a drying trend over the past century. High spatial correlation between coral δ18O and SST in the region of the Loop Current and Gulf Stream system suggests that Little Cayman is a sensitive location for detecting past large‐scale temperature variability beyond the Central Caribbean region. More specifically, our δ18O data track changes in North Atlantic Oscillation variability on decadal and multidecadal time scales providing insights into the temporal and spatial nonstationarity of the North Atlantic Oscillation. A combination of our δ18O record with two coral records from different Caribbean sites reveals high spatial correspondence between coral δ18O and SST variability in the North Atlantic subtropical gyre, where few instrumental measurements and proxies are available prior to the twentieth century. Our results clearly demonstrate the potential of combining proxy data to provide information from sparsely sampled areas, helping to reduce uncertainty in model‐based projections.

Newly released satellite data confirm that chlorofluorocarbons (CFCs) are the source of the chlorine that is eroding Earth's protective ozone layer. Three years' worth of data from the National Aeronautics & Space Administration's Upper Atmosphere Research Satellite (UARS) have enabled NASA scientists to prepare the first global maps of CFCs and their breakdown products in the stratosphere—hydrogen chloride (HCl) and hydrogen fluoride (HF). The maps refute the claims of skeptics that natural sources, not human activities, cause ozone depletion. We believe these data eliminate the possibility [that] there are major natural sources of chlorine in the stratosphere, says UARS project scientist Mark Schoeberl. They confirm CFCs are responsible for the ozone loss we are observing. Critics of the theory that chlorine from CFCs catalyzes ozone depletion argue CFC molecules are too heavy to rise into the stratosphere. And even if they did, the skeptics say, the amount of chlorine CFCs carry into the stratosphe...

Seasonal variations in the phytoplankton biomass and productivity of a warm-core Gulf Stream ring

Qualitative and quantitative changes in the freshwater phytoplankton from one of the largest lakes in Potter Peninsula were studied during the summer period of 1995/1996. The main limnological features were analysed. This research constitutes the first study dealing with the phytoplankton structure and dynamics from lakes in Potter Peninsula. Due to the mixing of the water column by the constant wind action during the ice-free period, neither physical, chemical nor biological parameters showed differences between depths. Soluble reactive phosphorus remained low (26 μg l−1) while total phosphorus concentrations were up to 232 μg l−1. Suspended solids and total phosphorus differed significantly between the two basins in which the lake is divided. Sixty-five taxa were identified. The Bacillariophyceae was the dominant class followed by Chrysophyceae. Achnanthes lanceolata var. haynaldii and Hydrurus foetidus (cysts) were the dominant species. Tychoplanktonic species were the best represented in terms of abundance and species richness. The principal component analysis carried out with abiotic variables showed a temporal gradient characterised by the augmentation of suspended solids, total phosphorus, conductivity, pH and NH4-N to the end of the summer period. The Principal Component Analysis performed with biotic variables also showed a temporal trend related to a decline in phytoplankton density and an enhancement of chlorophyll-a despite a slight increase of light limitation during the study period. This inverse relation may be due to the presence of picoplankton in chlorophyll-a samples. The potential effect of grazing on the phytoplankton structure is a subject to be tested in future studies.

A set of algorithms was combined for a simple derivation of land surface albedo from measurements of the Advanced Very High Resolution Radiometer (AVHRR) on board NOAA satellites. The system consists of a narrow-to-broadband conversion and bi-directional correction at the top of the atmosphere, and an atmospheric correction. We demonstrate the results with one month worth of data from the NOAA/NESDIS global vegetation index (GVI) weekly dataset and the NOAA/NASA pathfinder atmosphere (PATMOS) project daily data with the original global area coverage (GAC) resolution. Error analysis of the methodology indicates that the surface albedo can be retrieved with 15-20% relative accuracy. Monthly albedos derived from September 1989 GVI and PATMOS data agree well except for small discrepancies attributed mainly to different cloud screening techniques. 5-year mean September albedos derived from the GVI multi-annual time series are consistent with those derived from low-resolution Earth Radiation Budget Experiment data as well as with a September map compiled from ground observations and used in many numerical weather and climate models. Instantaneous GVI-derived albedos were validated against surface measurements. The discrepancies were found to be within the expected 15% relative error, and a 1-2% absolute bias can be attributed to differences in areal coverage and representativeness of the satellite and ground data. The presented pilot study is a prototype for a real-time production of global surface albedo maps from the original GAC resolution data within the NOAA/NESDIS modernized AVHRR processing system (MAPS).

Surface phytoplankton pigment distributions in the Atlantic Ocean: an assessment of basin scale variability between 50°N and 50°S