Changes In Phytoplankton Production Research Articles

Variability of Primary Productivity as an Initial Link in Carbon Flux Under the Influence of Hydrological Conditions in the Baltic Sea

Investigating variability in phytoplankton primary productivity as a key component of the “biological pump” is critical to quantifying flux in the marine environment. We hypothesized that under certain hydrological conditions, changes in phytoplankton productivity are greater with changes in photosynthetic efficiency (the ratio of primary production (P P ) to the rate of electron transport in the phytoplankton photosystem, P P /ETR) than with changes in chlorophyll content. This study showed that increase of P P during sharp changes in hydrological parameters in the temporary frontal South-East Baltic (SEB) is achieved by increasing the efficiency of photosynthesis, i.e., the degree of use of light energy captured by chlorophyll a (Chl a). In the Gulf of Finland (GF), an increase in P P followed an increase in salinity from the Neva mouth to the sea and controls chlorophyll contents with low variability in photosynthetic efficiency. For SEB and GF, measurements of parameters of phytoplankton productivity and chlorophyll a content in late autumn (November) are carried out. The first stage of carbon flow (in biological pump), expressed in terms of primary production, was higher in the SEB than in the GF

Control Mechanisms of Primary Productivity Revealed by Calcareous Nannoplankton From Marine Isotope Stages 12 to 9 at the Shackleton Site (IODP Site U1385)

AbstractNowadays, primary productivity variations at the SW Iberian Margin (IbM) are primarily controlled by wind‐driven upwelling. Thus, major changes in atmospheric circulation and wind regimes between the Marine Isotope Stages (MIS) 12 and 9 could have driven substantial changes in phytoplankton productivity which remains poorly understood. We present a high‐resolution calcareous nannofossil record from the Shackleton Site Integrated Ocean Discovery Program Site U1385 that allow the assessment of primary productivity and changing surface conditions on orbital and suborbital timescales over the SW IbM. These records are directly compared and integrated with terrestrial – Mediterranean forest pollen – and marine – benthic and planktic oxygen stable isotopes (δ18O), alkenone concentration [C37], Uk´37‐Sea Surface Temperature and % C37:4 – proxy records from Site U1385. Our results indicate intra‐interglacial increase in primary productivity together with intensification of the Azores anticyclonic high‐pressure cell beyond the summer that suggests a two‐phase upwelling behavior during the full interglacial MIS 11c (∼420–397 ka), potentially drived by atmospheric NAO‐like variability. Primary productivity is largely enhanced during the inception of glacial MIS 10 and the early MIS 10 (∼392–356 ka), linked to intensified upwelling and associated processes during a period of strengthened atmospheric circulation. In agreement with the conditions observed during Heinrich events of the last glacial cycle, primary productivity reductions during abrupt cold episodes, including the Heinrich‐type (Ht) events 4 to 1 (∼436, 392, 384 and 339 ka) and the Terminations V and IV, seems to be the result of halocline formation induced by meltwater arrival, reducing the regional upward nutrient transference.

Changes in chlorophyll concentration and phenology in the North Sea in relation to de‐eutrophication and sea surface warming

AbstractAt least two major drivers of phytoplankton production have changed in recent decades in the North Sea: sea surface temperature (SST) has increased by ~ 1.6°C between 1988 and 2014, and the nitrogen and phosphorus loads from surrounding rivers have decreased from the mid‐1980s onward, following reduction policies. Long time series spanning four decades (1975–2015) of nutrients, chlorophyll (Chl), and pH measurements in the Southern and Central North Sea were analyzed to assess the impact of both the warming and the de‐eutrophication trends on Chl. The de‐eutrophication process, detectable in the reduction of nutrient river loads to the sea, caused a decrease of nutrient concentrations in coastal waters under riverine influence. A decline in annual mean Chl was observed at 11 out of 18 sampling sites (coastal and offshore) in the period 1988–2016. Also, a shift in Chl phenology was observed around 2000, with spring bloom formation occurring earlier in the year. A long time series of pH in the Southern North Sea showed an increase until the mid‐1980s followed by a rapid decrease, suggesting changes in phytoplankton production that would support the observed changes in Chl. Linear correlations, however, did not reveal significant relationships between Chl variability and winter nutrients or SST at the sampling sites. We propose that the observed changes in Chl (annual or seasonal) around 2000 are a response of phytoplankton dynamics to multiple stressors, directly or indirectly influenced by de‐eutrophication and climate warming.

Seasonal variability of the carbon export in the central South China Sea

The South China Sea (SCS) is strongly influenced by the East Asian monsoon system with seasonal reversal. Measurements from a 7-year continuous sediment trap located in the central SCS showed a clear seasonal pattern. The particulate organic carbon (POC) export flux at the depth of 1200 m was considerably higher in monsoon seasons. The driving dynamics leading to this seasonal variability of POC export, however, remains inadequately understood. Here, a one-dimensional physical-biogeochemical coupled model was developed to simulate the temporal variability of a lower-trophic planktonic ecosystem. The modeled POC export flux compared reasonably well with the 7-year time series from moored sediment trap. Model results showed that the POC export flux at 1200 m is highly correlated with the 0–100 m integrated primary productivity and with the export flux at 100 m, implying that the seasonal variability of sediment trap data could be induced by changes in phytoplankton production and its vertical export. Further model analysis suggested that the annual mean export ratio (e-ratio) at 100 m and transfer efficiency at 1200 m in the central SCS were 0.19 and 0.07, respectively, which are lower than those in high latitudes. The winter monsoon favors not only surface carbon fixation but also export to the deep ocean. The heat flux is the dominant factor regulating the seasonal cycle of mixed layer depth, nutrient supply, and the growth of phytoplankton in this region. The wind-driven mixing can further facilitate upward nutrient transport to the surface and amplify the seasonal amplitude of the POC export flux.

Changes in phytoplankton production and upwelling intensity off A Coru\xf1a (NW Spain) for the last 28\xa0years

The analysis of a 28-year-long (1989–2016) series of monthly measurements of chlorophyll concentrations and primary production rates at a shelf station off A Coruña (NW Spain) provided evidence of changes at several time scales that were only partly related to upwelling intensity. Chlorophyll determinations were made in acetonic extracts and primary production rates by the measurement of 14C-uptake by natural phytoplankton populations in simulated in situ conditions. Wavelet analysis revealed multiple modes of variation in both series, particularly at high frequencies, but some were only significant for part of the series. For instance, the seasonal cycle was not uniform through the series despite the annual repetition of maxima and minima. At multiannual time scales, both series were divided in three quasi-decadal periods characterized by significant increases in mean values. Fluctuations in chlorophyll and primary production covaried with changes in upwelling intensity at annual scales, but annual means showed low correlation. Changes in dissolved nutrient concentrations from continental sources were the likely drivers of the observed changes in productivity at large time scales. Increases in the decadal mean rates of production and concentrations of chlorophyll were driven by increased intensity of spring blooms associated to increased nutrients and low salinity water in the surface. In contrast, blooms caused by upwelling nutrients remained unchanged along the series. This study illustrates the complexity of interactions in coastal upwelling areas at large time scales, where changes in continental nutrient inputs may affect phytoplankton production more than variations in upwelling intensity.

Changes in phytoplankton productivity with the introduction of heavy metals into the ecosystem and its subsequent purifi cation with a humic sorbent

Mesoscale modeling experiments simulating water pollution of a freshwater plain reservoir by infusion of a mixture of heavy-metal (Cd, Zn, Cu) salts were conducted. Central to the research was determining the phytoplankton response (in terms of primary production) to the presence of heavy metals in water and to the introduction of a sorbent based on mechanochemically oxidized humic acids. The removal of heavy metals by phytoplankton on the 16th day of the experiment resulted in a decrease in the content of Cd(II) to 62%, Zn(II) to 58%, and Cu(II) to 46% of the initial levels. The use of sorbent under the same conditions led to a decrease in the content of Cd(II) to 21%, Zn(II) to 27%, and Cu(II) to 10% of the initial levels. The sorbent under study does not cause blooming of the reservoir, distinguishing it from sorbents containing humic acids with the native structure of molecules.

Changes in Phytoplankton Production after the Introduction of Heavy Metals into Ecosystem with Subsequent Cleaning by Humic Sorbent

The paper presents the results of experiments with mesomodeling of water pollution in a lowland freshwater body by a mixture of salts of heavy metals (Cd, Zn, Cu). The response of phytoplankton (in terms of primary production characteristics) to the presence of heavy metals in water and to the introduction of a sorbent based on mechanochemically oxidized humic acids has been studied. The removal of heavy metals by phytoplankton on the 16th day of the experiment has reduced the concentration of Cd(II) to 62, Zn(II) to 58- and Cu(II) to 46% of their initial levels. The application of a sorbent under the same conditions has led to a decrease in the concentration of Cd(II) to 21, Zn(II) to 27, and Cu(II) to 10% of the initial level. The examined sorbent does not cause blooming in the water body, thus it differs from the sorbents that contain humic acids with a native structure of molecules.

Effects of warming and eutrophication on coastal phytoplankton production

Phytoplankton production in coastal waters influences seafood production and human health and can lead to harmful algal blooms. Water temperature and eutrophication are critical factors affecting phytoplankton production, although the combined effects of warming and nutrient changes on phytoplankton production in coastal waters are not well understood. To address this, phytoplankton production changes in natural waters were investigated using samples collected over eight months, and under 64 different initial conditions, established by combining four different water temperatures (i.e., ambient T, +2, +4, and + 6 °C), and two different nutrient conditions (i.e., non-enriched and enriched). Under the non-enriched conditions, the effect of warming on phytoplankton production was significantly positive in some months, significantly negative in others, or had no effect. However, under enriched conditions, warming affected phytoplankton production positively in all months except one, when the salinity was as low as 6.5. These results suggest that nutrient conditions can alter the effects of warming on phytoplankton production. Of several parameters, the ratio of initial nitrate concentration to chlorophyll a concentration [NCCA, μM (μg L−1)−1] was one of the most critical factors determining the directionality of the warming effects. In laboratory experiments, when NCCA in the ambient or nutrient-enriched waters was ≥1.2, warming increased or did not change phytoplankton production with one exception; however, when NCCA was <1.2, warming did not change or decreased production. In the time series data obtained from the coastal waters of four target countries, when NCCA was 1.5 or more, warming increased phytoplankton production, whereas when NCCA was lower than 1.5, warming lowered phytoplankton production, Thus, it is suggested that NCCA could be used as an index for predicting future phytoplankton production changes in coastal waters.

Influence of dimethyl sulfide on the carbon cycle and biological production

Dimethyl sulfide (DMS) is a significant source of marine sulfate aerosol and plays an important role in modifying cloud properties. Fully coupled climate simulations using dynamic marine ecosystem and DMS calculations are conducted to estimate DMS fluxes under various climate scenarios and to examine the sign and strength of phytoplankton-DMS-climate feedbacks for the first time. Simulation results show small differences in the DMS production and emissions between pre-industrial and present climate scenarios, except for some areas in the Southern Ocean. There are clear changes in surface ocean DMS concentrations moving into the future, and they are attributable to changes in phytoplankton production and competition driven by complex spatially varying mechanisms. Comparisons between parallel simulations with and without DMS fluxes into the atmosphere show significant differences in marine ecosystems and physical fields. Without DMS, the missing subsequent aerosol indirect effects on clouds and radiative forcing lead to fewer clouds, more solar radiation, and a much warmer climate. Phaeocystis, a uniquely efficient organosulfur producer with a growth advantage under cooler climate states, can benefit from producing the compound through cooling effects of DMS in the climate system. Our results show a tight coupling between the sulfur and carbon cycles. The ocean carbon uptake declines without DMS emissions to the atmosphere. The analysis indicates a weak positive phytoplankton-DMS-climate feedback at the global scale, with large spatial variations driven by individual autotrophic functional groups and complex mechanisms. The sign and strength of the feedback vary with climate states and phytoplankton groups. This highlights the importance of a dynamic marine ecosystem module and the sulfur cycle mechanism in climate projections.

Contrasting interannual changes in phytoplankton productivity and community structure in the coastal Canadian Arctic Ocean

AbstractThe rapid physical changes affecting the Arctic Ocean alter the growth conditions of primary producers. In this context, a crucial question is whether these changes will affect the composition of phytoplankton communities, augment their productivity, and eventually enhance food webs. We combined satellite and model products with in situ datasets collected during fall and provide new insights into the response of phytoplankton biomass and production in the Canadian Arctic by comparing an interior shelf (Beaufort Sea) and an outflow shelf (Baffin Bay). Correlation analysis was used to distinguish between seasonal and interannual variability and revealed that most biological variables are responding to the interannual pressures of climate change. In southeast Beaufort Sea, a change in phytoplankton community composition occurred, with a significant increase in diatoms from 2% (2002) to 37% (2010–2011) of the total protist abundance. In 2011, photosynthetic picoeukaryotes were twice as abundant as in 2002. For these two phytoplankton groups, abundance was correlated with the duration of the open‐water period, which also increased and affected vertical stratification and sea‐surface temperature. In contrast, there was a sharp decline in centric diatom abundance as well as in phytoplankton biomass and production in northern Baffin Bay over the years considered. These decreases were linked to changes in seasonal progression and sea‐ice dynamics through their impacts on vertical stratification and freshwater input. Overall, our results highlight the importance of stratification and the duration of the open‐water period in shaping phytoplankton regimes—either oligotrophic or eutrophic—in marine waters of the Canadian Arctic.

Phytoplankton response to whole lake inorganic N fertilization along a gradient in dissolved organic carbon.

Global change has increased inorganic nitrogen (N) and dissolved organic carbon (DOC; i.e., "browning") inputs to northern hemisphere boreal lakes. However, we do not know how phytoplankton in nutrient poor lake ecosystems of different DOC concentration respond to increased N availability. Here, we monitored changes in phytoplankton production, biomass and community composition in response to whole lake inorganic N fertilization in six boreal unproductive Swedish lakes divided into three lake pairs (control, N enriched) at three DOC levels (low, medium, high), with one reference year (2011) and 2 impact yr (2012, 2013). We found that phytoplankton biomass and production decreased with DOC concentration before N fertilization. Further, phytoplankton community composition also differed with respect to DOC, with a dominance of non-flagellated autotrophs at low DOC towards an increasing dominance of flagellated autotrophs with increased lake DOC concentration. The N fertilization increased phytoplankton biomass and production in all lakes, but did not affect phytoplankton community composition. However, the net response in biomass and production to N fertilization declined with increasing DOC, implying that the lake DOC concentration is critical in order to infer phytoplankton responses to N fertilization, and that the system switches from being primarily nutrient limited to becoming increasingly light limited with increased DOC concentration. In conclusion, our results show that browning will reduce phytoplankton production and biomass and influence phytoplankton community composition, whereas increased inorganic N loadings from deposition, forestry or other land use will primarily enhance phytoplankton biomass and production. Together, any change in the landscape that enhances inorganic N availability will increase phytoplankton production and biomass, but the positive effects of N will be much weaker or even neutralized in browner lakes as caused by light limitation.

Carbon dioxide emissions and sediment organic carbon burials across a gradient of trophic state in eleven New Zealand lakes

Lakes are known to be important to the global carbon balance as they are both CO2 sources to the atmosphere and also accumulate large amounts of carbon in their sediment. CO2 flux dynamics across the air–water interface in 11 lakes of varying trophic state in the Rotorua region, New Zealand, derived from measured alkalinity, pH and wind speed at given temperature, showed that lakes may shift from being atmospheric CO2 sources to sinks due to seasonal changes in phytoplankton productivity and lake mixing dynamics. Decreases in trophic state (i.e. improved water quality) in some of the lakes over the eight-year monitoring period were associated with increased surface water CO2 concentrations and, as a consequence, increased CO2 flux to the atmosphere. Organic carbon content analysis of the bottom sediments revealed that lakes with high phytoplankton productivity, indicated by high chlorophyll a biomass, generally had high rates of carbon deposition to the sediments, but not all deposited carbon was permanently buried. Remineralization of the organic carbon accrued in productive lakes may potentially generate CO2, as well as CH4, which promotes these lakes to act as greenhouse gas emitters.

Southern Ocean Phytoplankton in a Changing Climate

Phytoplankton are the base of the Antarctic food web, sustain the wealth and diversity of life for which Antarctica is renowned, and play a critical role in biogeochemical cycles that mediate global climate. Over the vast expanse of the Southern Ocean (SO), the climate is variously predicted to experience increased warming, strengthening wind, acidification, shallowing mixed layer depths, increased light (and UV), changes in upwelling and nutrient replenishment, declining sea ice, reduced salinity, and the southward migration of ocean fronts. These changes are expected to alter the structure and function of phytoplankton communities in the SO. The diverse environments contained within the vast expanse of the SO will be impacted differently by climate change; causing the identity and the magnitude of environmental factors driving biotic change to vary within and among bioregions. Predicting the net effect of multiple climate-induced stressors over a range of environments is complex. Yet understanding the response of SO phytoplankton to climate change is vital if we are to predict the future state/s of the ecosystem, estimate the impacts on fisheries and endangered species, and accurately predict the effects of physical and biotic change in the SO on global climate. This review looks at the major environmental factors that define the structure and function of phytoplankton communities in the SO, examines the forecast changes in the SO environment, predicts the likely effect of these changes on phytoplankton, and considers the ramifications for trophodynamics and feedbacks to global climate change. Predictions strongly suggest that all regions of the SO will experience changes in phytoplankton productivity and community composition with climate change. The nature, and even the sign, of these changes varies within and among regions and will depend upon the magnitude and sequence in which these environmental changes are imposed. It is likely that predicted changes to phytoplankton communities will affect SO biogeochemistry, carbon export, and nutrition for higher trophic levels.

East Asian winter monsoon controlling phytoplankton productivity and community structure changes in the southeastern South China Sea over the last 185 kyr

The South China Sea (SCS) is one of the largest marginal seas in the world and it plays an important role in regional climate change and carbon cycles. However, mechanisms of glacial–interglacial phytoplankton productivity changes remain under-studied, especially for the southeastern SCS. In this study, the productivity record for the southeastern SCS (core MD972142) over the last 185kyr was generated using multiple biomarkers, including C37 alkenones (C37:2+C37:3), brassicasterol, dinosterol, and alkyl diols (C30+C32) as productivity proxies for haptophytes, diatoms, dinoflagellates, and eustigmatophytes (and diatoms), respectively. All biomarker contents indicate higher individual as well as total phytoplankton productivities during peak glacials than during interglacials. Our records afford a better constraint on spatial pattern of glacial productivity changes, which suggest that both the southeastern and northern SCS glacial productivity increases were controlled by the stronger East Asian winter monsoon (EAWM), which brought more nutrients to the surface through stronger mixing of nutrient-rich deep waters. Biomarker ratios reveal a relatively stable phytoplankton community structure (PCS), but relative diatom productivity was higher during glacials. The PCS record is consistent with stronger EAWM forcing during glacials, which supplied nutrients to the surface with relatively stable composition. The decrease of C37 alkenones during the last 120kyr is likely a global phenomenon, which could be related to the evolution of the haptophytes. In the SCS, this trend was also likely caused by changes of subsurface nutrient supply to the SCS, which significantly modulated the PCS by a gradual decrease of haptophyte contribution to total phytoplankton in the northern and southeastern SCS since MIS 5.

Changes in phytoplankton productivity and community structure in the northern South China Sea during the past 260 ka

A high-resolution molecular organic geochemical study of core MD05-2904 reveals changes in the productivity and community structure of paleo-phytoplankton during the last 260ka in the northern South China Sea (SCS). Multiple biomarkers, including C37 alkenones, dinosterol, brassicasterol and C30 diols, are used as representatives of haptophytes, dinoflagellates, diatoms and eustigmatophytes, respectively. The abundances and mass accumulation rates of biomarkers indicate that phytoplankton productivity was relatively higher during glacial periods than during interglacial periods. However, the phytoplankton community structure, inferred from the relative abundance of biomarkers, does not display any evident glacial/interglacial cycles. In agreement with previous studies, our results also suggest a linkage between the increased paleo-productivity and the enhanced East Asian winter monsoon in the glacial northern SCS. The relatively stable PCS may reflect a lack of sensitivity of the phytoplanktonic groups to variations of nutrient composition on glacial/interglacial and shorter time scales. A long-term decrease in the C37 alkenone abundance since MIS 5 might have been related to the increasing influence of the northward intrusion of Antarctic Intermediate Water and/or sub-Antarctic Mode Water on the SCS thermocline waters. Moreover, the evolution of alkenone producers and changes in the coccolithophore genera on C37 alkenones might also have contributed to the long-term decrease in the C37 alkenone abundance.

Potential consequences of climate change for primary production and fish production in large marine ecosystems

Existing methods to predict the effects of climate change on the biomass and production of marine communities are predicated on modelling the interactions and dynamics of individual species, a very challenging approach when interactions and distributions are changing and little is known about the ecological mechanisms driving the responses of many species. An informative parallel approach is to develop size-based methods. These capture the properties of food webs that describe energy flux and production at a particular size, independent of species' ecology. We couple a physical–biogeochemical model with a dynamic, size-based food web model to predict the future effects of climate change on fish biomass and production in 11 large regional shelf seas, with and without fishing effects. Changes in potential fish production are shown to most strongly mirror changes in phytoplankton production. We project declines of 30–60% in potential fish production across some important areas of tropical shelf and upwelling seas, most notably in the eastern Indo-Pacific, the northern Humboldt and the North Canary Current. Conversely, in some areas of the high latitude shelf seas, the production of pelagic predators was projected to increase by 28–89%.

Eastern Equatorial Pacific productivity and related-CO 2 changes since the last glacial period

Understanding oceanic processes, both physical and biological, that control atmospheric CO(2) is vital for predicting their influence during the past and into the future. The Eastern Equatorial Pacific (EEP) is thought to have exerted a strong control over glacial/interglacial CO(2) variations through its link to circulation and nutrient-related changes in the Southern Ocean, the primary region of the world oceans where CO(2)-enriched deep water is upwelled to the surface ocean and comes into contact with the atmosphere. Here we present a multiproxy record of surface ocean productivity, dust inputs, and thermocline conditions for the EEP over the last 40,000 y. This allows us to detect changes in phytoplankton productivity and composition associated with increases in equatorial upwelling intensity and influence of Si-rich waters of sub-Antarctic origin. Our evidence indicates that diatoms outcompeted coccolithophores at times when the influence of Si-rich Southern Ocean intermediate waters was greatest. This shift from calcareous to noncalcareous phytoplankton would cause a lowering in atmospheric CO(2) through a reduced carbonate pump, as hypothesized by the Silicic Acid Leakage Hypothesis. However, this change does not seem to have been crucial in controlling atmospheric CO(2), as it took place during the deglaciation, when atmospheric CO(2) concentrations had already started to rise. Instead, the concomitant intensification of Antarctic upwelling brought large quantities of deep CO(2)-rich waters to the ocean surface. This process very likely dominated any biologically mediated CO(2) sequestration and probably accounts for most of the deglacial rise in atmospheric CO(2).

Historical trends of hypoxia in Changjiang River estuary: Applications of chemical biomarkers and microfossils

Over the past two decades China has become the largest global consumer of fertilizers, which has enhanced river nutrient fluxes and caused eutrophication and hypoxia in the Yangtze (Changjiang) large river delta-front estuary (LDE). In this study, we utilized plant pigments, lignin-phenols, stable isotopes (δ 13C and δ 15N) and foraminiferal microfossils in 210Pb dated cores to examine the history of hypoxia in the Changjiang LDE. Two sediment cores were collected onboard R/V Dong Fang Hong 2 using a stainless-steel box-corer; one at a water depth of 24.7 m on Jun. 15, 2006 and the other at 52 m on Nov. 20, 2007, both in the hypoxic region off the Changjiang LDE. There has been a significant increase in the abundance of plant pigments after 1979 that are indicators of enhanced diatom and cyanobacterial abundance, which agrees with post-1980 record of increasing nutrient loads in the Changjiang River. The increased inputs of terrestrially derived materials to the LDE are largely woody plant sources and most likely due to deforestation that began in the early 1950s. However, post-1960 lignin data did not reflect enhanced loading of woody materials despite continued deforestation possibly due to increased trapping from greater dam construction, a reduction of deforestation in the drainage basin since the last 1990s, and soil conservation practices. The lack of linkages between bulk indices (stable isotopes, % OC, molar C/N ratios) and microfossil/chemical biomarkers may reflect relative differences in the amount of carbon tracked by these different proxies. Although NO 3 − is likely responsible for most of the changes in phytoplankton production (post 1970s), historical changes in N loading from the watershed and hypoxia on the LDE shelf may not be as well linked in East China Sea (ECS) sediments due to possible denitrification/ammonification processes; finally, increases in low-oxygen tolerant foraminiferal microfossils indicate there has been an increase in the number of hypoxic bottom water events on the Changjiang LDE over the past 60 years.

Effect of atmospheric CO 2 and solar activity on wind regime and water column stability in the major global upwelling areas

It is not clear whether global warming will favour or reduce global ocean phytoplankton productivity in coastal areas. Moreover, the relative contributions made by natural and/or anthropogenic factors to possible changes in phytoplankton productivity are not clear. As the relationship between primary production and alongshore wind forcing is well established for the Eastern Boundary Current (EBC) ecosystems, our aim is to determine whether the changes experienced over the last five decades (1958–2007) in atmospheric CO 2 and solar activity have been able to affect the wind regime and water column stability in the most biologically productive upwelling areas of California, Canary, Humboldt and Benguela. We approached the work by statistically studying the effect of solar activity and atmospheric CO 2 on surface alongshore wind stress and on water column stability. There was an increasing trend in wind stress and water column stability in all the upwelling areas over the period studied (with the single exception of stability in the California EBC system). The analysis of detrended series evidenced significant relationships between atmospheric CO 2 concentration and wind stress and water column stability in the coastal upwelling areas investigated. In addition, wind stress and stability data were found to be consistent, with negative linear relationships between wind stress and CO 2 in most of the sites in the Benguela, Canary and Humboldt regions associated, as expected, to positive relationships when water column stability is used as regressand. The results of the present study suggest that greenhouse gas forcing, independent of its well known general increasing trend, was able to decrease wind stress intensity and increase water column stability for the period 1958 to present in most of the sites of the four Eastern Boundary Ecosystems studied, with the one exception of the California region. Conversely, the impact of solar activity appeared to be quite low compared to the greenhouse gas forcing.

Carbon cycling in Lake Erie during cultural eutrophication over the last century inferred from the stable carbon isotope composition of sediments

A ~106-cm sediment core from the eastern basin of Lake Erie was examined to investigate biogeochemical processes in this large lake during its cultural eutrophication over the last century. We measured stable carbon isotopes of total organic carbon and calcium carbonate (δ13CTOC and \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \)) as well as the concentrations of total organic carbon (TOC) and calcium carbonate (CaCO3). δ13CTOC and TOC show a strong positive correlation throughout the core and record changes in phytoplankton productivity and nutrient loading. CaCO3 and TOC concentrations display a negative correlation throughout the core, suggesting that CaCO3 concentrations are controlled primarily by decomposition of TOC in the hypolimnion and the sediments, although temperature and invasive mussels are also potential controlling factors. \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \) values show a positive correlation with δ13CTOC between 1909 and 1969, indicating phytoplankton productivity was the primary control for \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \) values during eutrophication. However, a negative correlation between \( \delta^{13} {\text{C}}_{{{\text{CaCO}}_{ 3} }} \) and δ13CTOC from 1970 to 2002 suggests that these two proxies tracked different aspects of the carbon cycle in the lake in more recent times. The cause for the negative correlation is not yet known, but it is perhaps associated with temperature variations and seasonal differences in productivity.