Distribución de pigmentos fotosintéticos del fitoplancton del Golfo de Tehuantepec en verano (junio, 2003): importancia del picofitoplancton*

Existen estudios previos sobre fitoplancton y sus grupos taxonómicos y especies, así como de su biomasa y productividad primaria, principalmente en invierno y primavera, pero se conoce poco la estructura del fitoplancton del Golfo de Tehuantepec en verano. Aquí se dan a conocer la composición y distribución de pigmentos fotosintéticos fitoplanctónicos en condiciones de verano. Se obtuvieron datos hidrográficos en nueve estaciones durante un crucero oceanográfico en junio, 2003, y se analizaron cinco pigmentos, Fucoxantina, Prasinoxantina, Violaxantina, Zeaxantina (indicador de Synechococcus, procarionte del picoplancton) y Divinil-clorofila a (diagnóstico de Prochlorococcus, otro procarionte del picoplancton). La columna de agua se encontró estratificada: la capa superficial, definida por la profundidad del tope de la termoclina, varió entre 20 y 35 m de espesor. Los valores de todos los pigmentos fueron bajos, pero mostraron patrones similares de distribución vertical, con un pico de concentración subsuperficial (entre 30 y 40 m), destacando Divinil-clorofila a en la mayoría de las estaciones, excepto en la 3 y 4, donde la Fucoxantina fue el principal pigmento. Estos picos no siempre coincidieron con la profundidad de la termoclina en cada estación, generalmente éstos se encontraron por debajo de ella. Este escenario muestra al picoplancton como una fracción importante en verano (al menos en junio), contrastando notablemente con la condición de invierno-primavera, de intensa mezcla turbulenta y surgencias, donde el microplancton y las diatomeas predominan

Sand deposits reveal great earthquakes and tsunamis at Mexican Pacific Coast

Globally, instrumentally based assessments of tsunamigenic potential of subduction zones have underestimated the magnitude and frequency of great events because of their short time record. Historical and sediment records of large earthquakes and tsunamis have expanded the temporal data and estimated size of these events. Instrumental records suggests that the Mexican Subduction earthquakes produce relatively small tsunamis, however historical records and now geologic evidence suggest that great earthquakes and tsunamis have whipped the Pacific coast of Mexico in the past. The sediment marks of centuries old-tsunamis validate historical records and indicate that large tsunamigenic earthquakes have shaken the Guerrero-Oaxaca region in southern Mexico and had an impact on a bigger stretch of the coast than previously suspected. We present the first geologic evidence of great tsunamis near the trench of a subduction zone previously underestimated as potential source for great earthquakes and tsunamis. Two sandy tsunami deposits extend over 1.5 km inland of the coast. The youngest tsunami deposit is associated with the 1787 great earthquake, M 8.6, producing a giant tsunami that poured over the coast flooding 500 km alongshore the Mexican Pacific coast and up to 6 km inland. The oldest event from a less historically documented event occurred in 1537. The 1787 earthquake, and tsunami and a probable predecessor in 1537, suggest a plausible recurrence interval of 250 years. We prove that the common believe that great tsunamis do not occur on the Mexican Pacific coast cannot be sustained

Application of multiple proxies in Mexican tropical coasts to prove evidence of tsunami deposits

"The study of tsunami deposits has significantly advanced since the Chilean 2010 and Tohoku 2011 tsunamis providing opportunities to analyze tsunami deposits and their characteristics (Rubin et al., 2017)." (fragm.

La biodiversidad marina: el caso de los ostrácodos

Ecological terms of recurrent use are presented, as for instance biota, biotopo, biocenosis, biotic, abiotic, ecosystem, biodiversity. The biological diversity of ostracoda (Crustacea) in the marine ecosystem is analysed, as well as the role it plays in plancton, bentos and necton, and its biology and habitats are discussed. The ICMyL, UNAM (México's National University) has carried out research, and about 760 species of ostracods have been reported, 300 in the Gulf of México, 110 in the Caribbean Sea and3 50 in the Pacific. The need for more research in the Pacific and the Caribbean Sea is emphasized.

Paleoceanographic evolution of the Gulf of Tehuantepec (Mexican Pacific) during the last ~6 millennia

Oceanographic dynamics in the Gulf of Tehuantepec (GT) are the direct consequence of climate variability, mainly influenced by the strong wind regime locally called “Tehuanos” and the interactions between the Intertropical Convergence Zone (ITCZ) and El Niño Southern Oscillation (ENSO). The area is characterized by intense upwelling driven by the Tehuanos within one of the largest Oxygen Minimum Zones (OMZ) in the world. Upwelling carries nutrient-rich subsurface waters to the surface and provides marine resources to the coasts conforming one of the main economic sectors in the region. In this study, sediment core MD02-2521 is used to perform the first high-resolution paleoceanographic reconstruction of the last 6 millennia in the GT. The main focus is put on the analysis of the benthic foraminifera (BF) assemblages inhabiting within the OMZ, which appear to respond to bottom oxygenation and climate variations of the last ~6000 years. The microfossil assemblages throughout the sediment core revealed, first, intervals where the lack of foraminifera provide evidence of episodes of strong deoxygenation that triggered the dissolution of calcareous foraminiferal tests, second, a long-term decline of bottom-water oxygenation in the last ~2500 years likely responding to the southward migration of the ITCZ. Last, variations in response to the transitions between cold and warm periods occurred during the last 2–2.5 millennia and cyclicities of 1470 years resembling Bond Cycles suggest a climatic connection between the Pacific and Atlantic Oceans during the late-Holocene

Paleoceanography of the Gulf of Tehuantepec during the Medieval Warm Period

The present study is focused on sediment core MD02–2521 in the Gulf of Tehuantepec (GT). This area, situated within the Oxygen Minimum Zone (OMZ), is rich in marine resources due to seasonal upwelling caused by the Tehuanos winds and a less deep thermocline representing an important economic sector of the region; however, has been the focus of a little number of studies. Benthic foraminifera (BF) are the target proxy to reconstruct bottom‑oxygen variability during the Medieval Warm Period (MWP), showing that this area was affected by cyclic variability of dissolved oxygen (DO) in 3 phases: higher, poorer, and oxygen-depleted shifting every ~90 years. The oxygen-depleted periods result in foraminiferal test dissolution, implying inevitable gaps of information. The MWP has been broadly identified as a warm anomaly in most parts of the globe and even compared with the current climate change to serve as analogous to predict future consequences. Opposing to the global warming stands, the Eastern Tropical North Pacific (ETNP) seems to have experienced a cooling trend. This study provides another proof that the MWP, besides that it is not a warm period everywhere, is also not homogeneous, so that quasi-centennial cycles may likely respond to solar activity and the dynamic interaction between decadal-to centennial phenomena such as the El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the seasonal migration of the Intertropical Convergence Zone (ITCZ)

Changes of bottom water oxygenation during the last half millennium in the Gulf of Tehuantepec (Eastern Tropical North Pacific): A multiproxy approach

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Diatom-based paleoproductivity and climate change record of the Gulf of Tehuantepec (Eastern Tropical Pacific) during the last ~500 years

International audienceChanges in marine productivity of the last five centuries in the Gulf of Tehuantepec were investigated using a high-resolution record of diatoms, organic carbon (C org ), total nitrogen (TN), Ni/Al, and Cu/Al. The laminated sediments were dated by using 210 Pb and 14 C, with a bayesian age model providing a new Δ R = 247 ± 30 years for the bulk sediment. The Little Ice Age (LIA) (~1500 to ~1858 CE) was characterized by the predominance of cold-water and high productivity diatoms ( Chaetoceros spores, Thalassionema nitzschioides, Lioloma pacificum, Thalassiosira nanolineata, and Rhizossolenia setigera) and high values of geochemical productivity proxies. A transition period (~1860 to ~1919 CE) toward warmer conditions related to the end of the LIA and the beginning of the Current Warm Period (CWP), was indicated by the appearance of warm-water diatoms ( Neodelphineis pelagica, Thalassiosira tenera, and Rhizossolenia bergonii), as well as lower values of C org , TN, Ni/Al, and Cu/Al. The most recent period of the CWP (~1920 CE to today) was characterized by the increased abundance warm-water taxa ( N. pelagica, Cymatodiscus planetophorus, T. tenera, Plagiogramma minus, Nitzschia interruptestriata, and R. bergonii), and by the prevalence of low values of C org , TN, Ni/Al, and Cu/Al. These changes in productivity during the LIA and CWP were likely driven by changes in solar irradiance and the migration of the Intertropical Convergence Zone. This study highlights the spatial extent of the LIA in the Eastern Tropical North Pacific and contributes to the knowledge of the productivity response to climate in tropical regions

Statistical identification of coastal hypoxia events controlled by wind-induced upwelling

International audienceCoastal areas are inhabited by a large fraction of the human population and provide many important ecosystem services, notably those related to fisheries. Hypoxia occurs when dissolved oxygen (DO) levels are so low that affect metabolic processes of many organisms, causing stress or even death. During the last decades, coastal hypoxia events have increased and nowadays these are one of the largest impacts of global change on coastal ecosystems. The entrance area of the Gulf of California is a region characterized by a shallow oxygen minimum zone and seasonal coastal upwelling events that may cause hypoxia by shoaling the oxycline. Under the hypothesis that some of the observed hypoxia episodes are controlled by coastal upwelling events, the objective of this work was to propose a novel statistical methodology to identify these events. From two oceanographic cruises, we observed the top of the oxycline depth at ∼30 m near the coast, while hypoxia was reached at ∼55 m. Also, DO time-series were recorded with autonomous sensors from early 2014 to late 2016 every 30 min in surface waters (5 m depth) off the Mazatlán City coastal zone (Mexico). This time series showed hypoxia events (and even anoxia, DO -1) at surface waters lasting from days to weeks. We propose a novel methodology to identify coastal hypoxia events controlled by coastal upwelling, which involves statistical and frequency analyses performed in conjunction with other physical variables such as sea surface temperature (SST), sea level, and the coastal upwelling index (CUI). Results confirmed that coastal wind-induced upwelling controls at least half of the hypoxia events identified. Further research is needed to understand the processes responsible for the other events, likely including mesoscale processes (such as eddies and internal waves) and the degradation of organic matter during eutrophic conditions. The methodology could be used in other eastern boundary upwelling systems of the world. These results should be of interest to coastal zone managers, local fishing communities, and the large fishing industry of this region to discriminate between natural and anthropogenic hypoxia events

Planktonic foraminiferal assemblages and particle fluxes at the entrance of the Gulf of California highlight the effects of the strong El Niño 2015-2016

International audienceThe impacts of El Niño 2015-2016 on planktonic foraminiferal assemblages and particle fluxes (total mass, organic carbon, total nitrogen, and carbonate) were analyzed in a sediment trap record located at the entrance of the Gulf of California from 2015 to 2019. Biweekly data of the sea surface temperature (SST) and sea surface chlorophyll-a (Chl-a) were obtained from satellite images (MODIS-AQUA) during this period. Particle fluxes and planktonic foraminiferal assemblages reflected the seasonal cycles of SST and phytoplankton biomass highlighting the effects of El Niño 2015-2016. During neutral and La Niña conditions, winter-spring upwelling leads to low SST, high Chl-a and particle fluxes, and an assemblage dominated by Globigerina bulloides while the summers are characterized by high SST, low Chl-a and particle fluxes, and a Globorotaloides hexagonus assemblage. In contrast, in normal summers, there is an alternation of G. bulloides and Orbulina universa-Trilobatus sacculifer-Globigerinella siphonifera associations. By late autumn under La Niña conditions, the Globigerinita glutinata assemblage reflects the transition from warm to cold conditions and the beginning of the upwelling season. This general pattern was affected by El Niño during 2015-2016. From late summer 2015 to early winter 2016 (El Niño 2015-2016 maximum intensity), Globigerinoides tenellus dominated, reflecting the intrusion of warm and oligotrophic equatorial waters. These results show the strong influence of El Niño Southern Oscillation (ENSO) on oceanic dynamics and planktonic foraminiferal assemblages at the entrance of the Gulf of California, and allow for a better interpretation of the preservation of these anomalous warm events in the sedimentary record, which can provide a better understanding of the long-term variations and effects of ENSO