Seasonal and interannual variability of satellite-derived chlorophyll pigment, surface height, and temperature off Baja California

Mean fields, seasonal cycles, and interannual variability are examined for fields of satellite-derived chlorophyll pigment concentrations (CHL), sea surface height (SSH), and sea surface temperature (SST) during 1997–2002. The analyses help to identify three dynamic regions: an upwelling zone next to the coast, the Ensenada Front in the north, and regions of repeated meanders and/or eddy variability west and southwest of Point Eugenia. High values of CHL are found in the upwelling zone, diminishing offshore. The exception is the area north of 31°N (the Ensenada Front), where higher CHL are found about 150 km offshore. South of 31°N, the long-term mean dynamic topography decreases next to the coast, creating isopleths of height parallel to the coastline, consistent with southward geostrophic flow. North of 31°N the mean flow is toward the east, consistent with the presence of the Ensenada Front. The mean SST reveals a more north-south gradient, reflecting latitudinal differences in surface heating due to solar radiation. Harmonic analyses and EOFs reveal the seasonal and interannual patterns, including the region of repeated eddy activity to the west and southwest of Point Eugenia. A maximum CHL occurs in spring in most of the inshore regions, reflecting the growth of phytoplankton in response to the seasonal maximum in upwelling-favorable winds. SST and SSH anomalies are negative in the coastal upwelling zone in spring, also consistent with a response to the seasonal maximum in upwelling. When the seasonal cycle is removed, the strongest signal in the EOF time series is the response to the strong 1997– 1998 El Niño, with a weaker signal representing La Niña (1998–1999) conditions. El Niño conditions consist of low chlorophyll, high SSH, and high SST, with opposite conditions during La Niña

Epidemiological implications of the genetic diversification of dengue virus (DENV) serotypes and genotypes in Mexico

Variation and clade shifts in dengue virus (DENV) genotypes are responsible for numerous dengue fever outbreaks throughout Latin America in the past decade. Molecular analyses of dengue serotypes have revealed extensive genetic diversification and the emergence of new genotypes in Brazil (DENV-4 genotype I) and elsewhere in tropical and subtropical America. The goal of the present study is to assess the extent to which the adventitious introduction of DENV genotypes and their increasing genetic diversity affects dengue epidemiology in Mexico. A nuanced sequence inspection and phylogenetic analysis of the C-prM nucleotide region of DENV was performed for specimens collecting in 2009 from the Veracruz State, Mexico. Findings were contrasted with specimens collected in adjacent years and analysed based on the epidemiological patterns reported between 1990 and 2019. Additionally, the identification process of various DENV genotypes was assessed, including: (1) DENV-1, genotype V, (2) the DENV-2 Asian/American and Asian II genotypes (3) DENV-3, genotype III, and (4) DENV-4, genotype I. This resulted in the discovery of a distinct genetic cladistic pattern for serotype DENV-2. Lastly, study findings suggest that a correlation exists between the emergence of novel genotypes and genetic diversification, with the increasing incidence of DENV infections in Mexico in 2009

Effects of mesoscale processes on phytoplankton chlorophyll off Baja California

Using satellite sea surface height (SSH) and chlorophyll (CHL), the year 2000 is analyzed to characterize the effects of mesoscale circulation patterns on phytoplankton spatial variability in the California Current (CC) off Baja California. Satellite data are combined with and compared to in situ field measurements (chlorophyll-a and hydrographic variables) along vertical alongshore sections located similar to 130 km offshore between similar to 24.5 degrees -33 degrees N. Monthly average maps of SSH and surface geostrophic velocities depict the characteristics of mesoscale meanders and eddies, which correspond well with the subsurface hydrographic and velocity fields. Satellite-derived pigment (CHL) represent in situ fields in the upper 0-20 m (overall r = 0.53; p < 0.05), but their representation of peak values in Deep Chlorophyll Maxima (DCM) at similar to 50 m depth are inaccurate. DCM are traced in all three seasons (January-July), descending from near the surface (north of 31 degrees N) to 50 m over a large extent of the transect to the south, approximately following the 24.7-25.1 isopycnals as they and the isotherms deepen to the south. In January, phytoplankton chlorophyll concentrations in the DCM are relatively uniform, originating during upwelling events that occur farther north, then following the equatorward flow of the CC. During April and July, the discrete maxima in the DCM occur at the centers of cyclonic meanders and the chlorophyll concentrations inside these maxima are enhanced as a result of local coastal upwelling off Baja California. Phytoplankton blooms created by coastal upwelling spread offshore and subduct along the 24.7-25.1 isopycnals, creating the DCM along the inner part of the meandering jet.KEYWORDS: Current system, Satellite, Pigment, State, Temperature, El Nino, Salinity, Evolution, Interannual variability, Coastal transition zon

Sea surface temperature patterns on the West Florida Shelf using growing hierarchical self-organizing maps

Author Posting. © American Meteorological Society 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 23 (2006): 325–338, doi:10.1175/JTECH1848.1.Neural network analyses based on the self-organizing map (SOM) and the growing hierarchical self-organizing map (GHSOM) are used to examine patterns of the sea surface temperature (SST) variability on the West Florida Shelf from time series of daily SST maps from 1998 to 2002. Four characteristic SST patterns are extracted in the first-layer GHSOM array: winter and summer season patterns, and two transitional patterns. Three of them are further expanded in the second layer, yielding more detailed structures in these seasons. The winter pattern is one of low SST, with isotherms aligned approximately along isobaths. The summer pattern is one of high SST distributed in a horizontally uniform manner. The spring transition includes a midshelf cold tongue. Similar analyses performed on SST anomaly data provide further details of these seasonally varying patterns. It is demonstrated that the GHSOM analysis is more effective in extracting the inherent SST patterns than the widely used EOF method. The underlying patterns in a dataset can be visualized in the SOM array in the same form as the original data, while they can only be expressed in anomaly form in the EOF analysis. Some important features, such as asymmetric SST anomaly patterns of winter/summer and cold/warm tongues, can be revealed by the SOM array but cannot be identified in the lowest mode EOF patterns. Also, unlike the EOF or SOM techniques, the hierarchical structure in the input data can be extracted by the GHSOM analysis.Support was provided by the Office of Naval Research under Grant N00014-98-1-0158 for observations and modeling of the west Florida continental shelf circulation and Grant N00014-02-1-0972 for the Southeast Atlantic Coastal Ocean Observing System

Hydrographic conditions near the coast of northwestern Baja California : 1997–2004

Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 26 (2006): 885-901, doi:10.1016/j.csr.2006.01.017.The effects of the 1997-98 and 2002-04 El Ni˜no on the upper waters in the con- tinental shelf and slope regions off northwestern Baja California are explored with data from eight cruises taken in late spring from 1998 to 2004 and the summers of 1997 and 1998. Geostrophic velocities were calculated referenced to a specific vol- ume anomaly surface separating the southward flowing California Current waters from the waters advected to the north by the California Undercurrent. The result- ing fields show equatorward flow near the surface except in the summer of 1997, when a poleward jet was found in the upper 40 dbars. This shallow jet advected anomalously warm and salty waters characteristic of the 1997-98 El Ni˜no, with its core found within 20-30 kms from the coast. By spring of 1998, the waters brought into the region by the jet had mixed across the pycnoline with the salty California Undercurrent waters below, resulting in high salinity levels on the density surfaces corresponding to the otherwise fresh California Current waters (25-26¾t). By con- trast, the 2002-04 El Ni˜no stands out for the very fresh and cold waters found on the same density surfaces in late spring of 2003 and 2004, marking a pronounced presence of subarctic waters. The fresh conditions found on the latter years repre- sent a nearshore expresion of the anomalous intrusion of subarctic waters observed 50-150 km from the coast of Southern California and Punta Eugenia, reported from July 2002 until April 2003. Our results suggest that the presence of this intrusion has continued to influence the region at least until May 2004.This work was supported by the US NSF (OCE-9986627 and OCE-0083976)

Response of the Shrimp Population in the Upper Gulf of California to Fluctuations in Dischergers of the Colorado River

Since 1935, the freshwater discharge from the Colorado River into the Gulf of California has decreased drastically, affecting the biological cycles of endemic species and other endangered species. In this study, a relationship was determined between the Colorado River freshwater discharge, the abundance of blue shrimp, Litopenaeus stylirostris (Stimpson, 1874) postlarvae, and the density of adult shrimp in the Upper Gulf of California (UGC). Data on Colorado River flow from 1904 to 2002, blue shrimp postlarvae from 1993 to 1997, and records of daily catches from pangas (small boats) of the commercial fleet operating in UGC from 1995 to 2002, were analysed. Catch per unit effort (CPUE) was used as a measure of the average daily density of adult shrimp. Two groups of CPUE and postlarvae abundance were found, with significant differences between them. The highest population density was observed in the years when the river flow was greater than 80 m3s−1. The lowest density was found for periods when the river flow was lower than 80 m3s−1. We conclude that the response of the shrimp population is non-linear and that postlarvae abundance and commercial fleet CPUE increased during the years in which freshwater discharge was highest, possibly because the habitat volume increased, consequently resulting in increased food availability for the shrimp

Atmosphere-ocean CO2 flux in the Gulf of California, Navachiste, Sinaloa

The CO2 fluxes were obtained in front of Navachiste Coastal System, Sinaloa in March 2017, a board a little ship from Laboratorio de Productividad Primaria y Sistema del Carbono (IPN-LPPSC)