1,721,138 research outputs found
EXPORT PRODUCTION OF COCCOLITHOPHORES IN AN UPWELLING REGION - RESULTS FROM SAN-PEDRO BASIN, SOUTHERN CALIFORNIA BORDERLANDS
No full textA seven month-long time series sediment trap project was carried out in San Pedro Basin (Southern California Borderlands) in order to evaluate the response of calcareous nannoplankton to seasonal hydrographic changes. This region is periodically influenced by upwelling, particularly during the spring and early summer. The highest fluxes of both whole coccospheres and individual coccoliths occurred during winter (January-February), a period when the fluxes of diatoms and planktic foraminifera were low. The highest coccolithophore fluxes were recorded in the mid-February with 860 × 106 coccoliths m−2 day−1, 8 × 106 whole coccospheres m−2 day−1, and 80 mg of coccolith carbonate m−2 day−1. Coccolith carbonate fluxes in January and February account for most of the total carbonate fluxes measured during this period. The season of maximum coccolithophore production in this region (winter) is correlated with weak stratification of the upper water column, low total primary production, low nutrient contents, and low temperatures.
Emiliania huxleyi and Florisphaera profunda are the two most abundant species in this region. While E. huxleyi displays no distinct seasonal changes in flux, F. profunda shows a clear preference for cold, low nutrient water conditions and low light levels. Helicosphaera spp. flux is positively correlated to the total coccosphere fluxes and is indicative of high coccolithophore productivity
Seasonal changes in coccolithophore densities in the Southern California Bight during 1991-1992
No full textSeasonal changes in coccolithophore cell densities in the San Pedro Basin, Southern California Bight, were investigated for the period October 1991 to September 1992. Coccolitho phore cell densities ranged from 6.3 × 104 coccospheres per liter in March 1992 to 0 cells per liter in November 1991. High coccolithophore concentrations occurred in late winter and spring, and low densities occurred in the summer and fall. The high coccolithophore densities during spring 1992 were associated with unusually low surface nutrient concentrations and a lack of upwelling, suggesting that the high densities were not part of a typical spring phytoplankton bloom in this region. We propose that the suppression of upwelling during spring 1992 may have been related to the prevailing ENSO conditions. Emiliania huxleyi type A dominated the total coccolithophore population throughout the year, Umbilicosphaera sibogae var. sibogae being the second most important contributor to the coccolithophore assemblage
Emiliania huxleyi calcite mass variability during periods of atmospheric CO2 rising in the Mediterranean Sea
No full textSolar forcing for nutricline depth variability inferred by coccoliths in the pre-industrial northwestern Mediterranean
Full text linkThe oceanic system has been rapidly changing under human-induced climate change that is taking place at unprecedented rates. The paleoclimate archive of the last two millennia is often adopted to discern the ongoing anthropogenic global warming from the pre-industrial natural climate variability. The Mediterranean Sea is an especially critical system, being particularly affected by climate change. A common group of marine unicellular planktonic calcifiers, coccolithophores, are forming calcite plates, coccoliths. When reaching the sediments, they have been employed as a proxy in many paleoenvironmental reconstructions and are increasingly used in the last centuries. Recent studies indicate a subtle response to historical climate changes, except for primary productivity switches during the Little Ice Age and, most importantly, across the Industrial age.
In this work, we use coccolith decadal-scale resolution data from core HER-MC-MR3.3, recovered in the Balearic Sea, exploring their variability over the pre-industrial age, from 700 BCE to 1740 CE. Results are compared to planktonic foraminifera stable isotopes, planktonic foraminiferal assemblages, alkenone-derived SSTs and foraminiferal Mg/Ca-derived SSTs, previously acquired in the same sediment core. Abundance variations in coccolith assemblages, expressed as Shannon-Wiener diversity H-index changes or as trends and fluctuations in ecological groups are associated with historical climate changes, among others the Medieval Climatic Anomaly and the Little Ice Age, indicating repeated modifications in surface water conditions, in response to hydrological and atmospheric changing patterns. A tight relationship between deep nutricline and upper water column stratified conditions, derived from high abundance of Florisphaera profunda, and high solar irradiation levels is established. The solar activity fingerprint in the F. profunda distribution pattern is further assessed by spectral analysis, with the emergence of significant periodicities observed in solar activity proxies, among others the well-known de Vries-Suess cycle. Finally, we notice small but statistically significant abundance fluctuations in holococcoliths (solution susceptible coccolith forms) that may be tied to their enhanced preservation during increased rainfall in western Europe. This implies the advection of westerlies and long-lasting blocking events that may have promoted deep-water formation and seafloor ventilation during this time. The comparison with sedimentological proxies of bottom current strength shows some inconsistencies but still defines variable and intermittent deep-water formation rates in the Gulf of Lions over the pre-industrial period
Mediterranean carbonate system dynamics and planktonic biocalcification during the last 19,000 years
No full textHistorical record of Corallium rubrum and its changing carbon sequestration capacity: A meta-analysis from the North Western Mediterranean
Full text linkBackground There is a scarcity of long time-span and geographically wide research on the health status of Corallium rubrum, including limited research on its historical ecology and carbon sequestration capacity. Objectives To reconstruct the temporal trends of the most reported C. rubrum population parameters in the Northwestern Mediterranean Sea and to determine the changes in total carbon sequestration by this species. Data sources Quantitative and qualitative, academic and grey documents were collected from scientific web browsers, scientific libraries, and requests to scientists. Study eligibility criteria Documents with original information of basal diameter, height and/or weight per colony, with a depth limit of 60 m in the Catalan and Ligurian Seas were analyzed. Synthesis methods We calculated yearly average values of C. rubrum biometric parameters, as well as estimated total weight, carbon flux, and carbon fixation in the structures of C. rubrum's colonies. Results In both study areas, the values of the selected morphometric parameters for C. rubrum decreased until the 1990s, then increased from the 2000s, with average values surpassing the levels of the 1960s (Ligurian Sea) or reaching levels slightly lower than those of the 1980s (Catalan Sea). The difference in carbon sequestered between the oldest (1960s: Ligurian Sea; 1970s: Catalan Sea) and the lowest (1990s) biomass value of colonies is nearly double. Limitations Quantitative data previous to the 1990s are very limited. Information on recent recovery trends in C. rubrum parameters is concentrated in a few areas and biased towards colonies in marine protected areas, with scarce quantitative information from colonies in other areas. Conclusions The halt in the C. rubrum decreasing trend coincided with the exhaustion of tree-like colonies and the first recovery response due to effective protection measures in some areas. Nevertheless, C. rubrum climate change mitigation capacity through carbon sequestration can be drastically reduced from its potential in only a few decades
Local and tourist perceptions of coastal marine habitats in Cap de Creus (NE Spain)
Full text linkDirect human pressure on Marine Protected Areas (MPAs) adds to climate change impacts on marine habitats, especially in coastal biodiversity hot spots. Understanding MPA user perception towards the Coastal marine Habitats (CMHs) could improve awareness of the challenges that such areas have to face, eventually providing insights for the design of conservation and tourism management plans. We studied perception of ecosystem services, impacts and threats of CMHs by locals and tourists (n = 624) of Cap de Creus MPA (NW Mediterranean Sea). Overall, we found that perceptions of tourists and locals are similar. Respondents perceived that CMHs provide valuable regulating services, and they assigned less value to cultural services. Locals valued the food provision ecosystem service of CMHs significantly more than tourists, probably because of the historical importance of fisheries for subsistence. Respondents ranked marine pollution of inland origin, climate change and people’s behaviour towards nature as the most impactful and threatening to CMHs, and invasive marine species as the least. Respondents also perceived that climate change impacts would increase soon, whilst the impact of people’s behaviour towards nature would decrease. Tourists perceived mass tourism as significantly more impactful and threatening to CMHs than locals did. Overall, our study shows that conservation of CMHs is highly valued, so more effort needs to be directed toward this goal
Calcareous nannofossil contribution to the carbonate export during the last 450 ka in the NW Pacific Ocean (Shatsky Rise).
No full textReventilation Episodes During the Sapropel S1 Deposition in the Eastern Mediterranean Based on Holococcolith Preservation
No full textOrganic-rich layers (sapropels), preserved in eastern Mediterranean marine sediment records, represent pronounced perturbations to thermohaline circulation and environmental conditions in the basin, in response to enhanced African monsoon activity and subsequent massive freshwater discharge. During the most recent event, Sapropel S1 formed between 10.8 and 6.1 ka, when freshwater-driven stratification caused seafloor anoxia below ~1,800-m depth, as a result of both failure of deep water formation and enhanced productivity. Here we analyze coccolith assemblages from the open eastern Mediterranean that form a west-east transect across the basin and provide insights on past environmental changes. We focus on holococcoliths, which are specifically produced by coccolithophores as part of their life cycle during the haploid phase. Since holococcolith calcification is characterized by nanocrystals highly susceptible to dissolution, we are testing their potential preservation under different bottom environmental conditions, including the effect of postdepositional oxidation. A comparison with benthic foraminifera assemblages in a core recovered close to Lybia reveals that holococcolith preservation is enhanced during seafloor reventilation and benthic foraminiferal repopulation in the middle to upper part of the record, before the actual sapropel termination. There are two such events of improved deep-water oxygenation in the Aegean and Adriatic Seas at 8.2 and 7.4 ka. The latter episode marks the onset of the transition to restored circulation in the eastern Mediterranean Sea, due to resumption of deep-water formation in the southern Aegean Sea and the conclusion of enhanced biogenic productivity
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