Sediment Transport Processes and Their Modelling Applications, 2013
ABSTRACT For sediment-transport models based on grain-size trend analysis there are consideration... more ABSTRACT For sediment-transport models based on grain-size trend analysis there are considerations that limit the inferences made about the net direction of the sediment transport. The most important limitation is the inability to validate the transport trends obtained with the hydrodynamic observations. We will use the LeRoux model to identify the dominant paths of sediment transport in Bahia Magdalena (upwelling subtropical system) and Bahia Chetumal (shallower tropical system). The grain-size trend was determined from 43 stations in Bahia Chetumal and 58 stations in Bahia Magdalena to identify the path of sediment transport. The analyses of principal components were used for the characteristics of the textural sediment in both studies. In Bahia Chetumal, the grain size and sorting explained at least 75% of the variance, with 20% of the variance explained by skewness. In Bahia Magdalena, the grain size and sorting explain 76% of the variance and skewness 22% of the variance. We established that the better-sorted sedimentary material is associated with stations with a fine grain-size and vice versa. The transport vectors suggest a net transport of sediment in the S-SE and S-SW directions, which is consistent with the direction of the surface and deep currents in Bahia Chetumal. The preferential deposition of fine and well-sorted material in the central part of the bay has an excellent correlation with the contents of anthropogenic pollutants found in other studies. The residual vectors of sediment transport in Bahia Magdalena suggest the presence of two gyres in the dispersion of the clastic material, a cyclonic-gyre in the central part and deeper portion and an anticyclonic-gyre in the southeast region of the bay. The pattern of sediment transport is consistent with the direction of the residual tidal currents in Bahia Magdalena. The contents of biogenic material found in this bay have an excellent correlation with the presence of these gyres and their preferential deposition.
Organic matter concentrations in a sediment core from the oxygen minimum zone (OMZ) off southern ... more Organic matter concentrations in a sediment core from the oxygen minimum zone (OMZ) off southern Baja California (705 m water depth) vary in concert with Dansgaard/Oeschger climate oscillations. A measure of sediment color (the third principal component of the diffuse ...
To monitor the composition and the vertical flux of particulate matter from the sea surface, a se... more To monitor the composition and the vertical flux of particulate matter from the sea surface, a sediment trap was moored in Cuenca Alfonso, Bahía de La Paz, a zone of high productivity in the southwestern Gulf of California. Carbonate-free samples from 2002 to 2005 were analyzed for C org, N, delta13C, and delta15N. The results show seasonal and interannual variability, with the delta13C and delta15N values larger in spring and summer than in fall and winter. The C:N ratio and delta13C increased by 1.5 units from 2002 to 2003-2005, suggesting a change in the supply of organic matter and-or the use or preferential degradation of N org. There was no interannual variation in delta15N. The occasional high delta15N values suggest that physical mechanisms, such as the shoaling and advection into the bay of 15N-rich subsurface equatorial water, occur over short time periods. The latter is presumed to be related to the periodic development of a significant cyclonic gyre in the southern Gulf.
The rates of accumulation of organic carbon, nitrogen and phosphorus (Corg, Norg, Porg), and of b... more The rates of accumulation of organic carbon, nitrogen and phosphorus (Corg, Norg, Porg), and of biogenic silica (BSi) were measured in sediment cores (GC31 and PC08) collected within the oxygen minimum zone of the Magdalena margin, off western Baja California Sur (Mexico). The rates of Corg, Norg and Porg accumulation were similar during marine isotopic stage 2 (MIS-2), the last glacial maximum (LGM) and the Late Holocene (LH, 3 kyrRecent), whereas the rate of BSi accumulation was greater during LGM and MIS-2 than during LH. In general, primary productivity during the MIS-2 and the LGM was similar to that observed during LH. The N/P ratio during the MIS-2 and the LGM was equivalent to that found during LH, suggesting that N and P were not limiting factors. In fact, the BSi/C ratio was relatively high (intense upwelling) when the N/P ratio was relatively low, indicating similar levels of primary productivity during the MIS-2, the LGM and LH. The results show that the productivity le...
The continental margin of the Northeast Pacific of Mexico (NEPM) is characterized by an oxygen mi... more The continental margin of the Northeast Pacific of Mexico (NEPM) is characterized by an oxygen minimum zone that allows the preservation and burial of organic carbon (Corg). In this work we evaluate the burial rate of sedimentary Corg of two cores (GC31 and PC08) collected from the Magdalena margin, Southern Baja California, Mexico. The flux of Corg in the Magdalena margin was compared with sedimentary records from the margins of Mazatlan and Gulf of Tehuantepec. The results indicate that the burial of Corg was larger during the Last Glacial maximum (LGM), of 800 mg/cm2/ka, and the Marine Isotope Stage-3 (MIS-3), of 900 mg/cm2/ka (with maximal values of 1400 mg/cm2/ka), than during the late Holocene (600 mg/cm2/ka), along the margin of the NEPM. These flux values of Corg indicate that the biological pump was 25 % more active during the LGM and 50% more efficient during the MIS-3 than during the late Holocene. The increase observed in the burial rates of Corg from low to mid latitude...
Hidrobiológica: [revista del Departamento de Hidrobiología]
The effects of increased salinity were evaluated on the ovum fertilization of the sea urchin spec... more The effects of increased salinity were evaluated on the ovum fertilization of the sea urchin species, Strongylocentrotus franciscanus Agassiz, 1863 and Lytechinus anamesus Clark, 1912, which were collected by means freediving in the bay Todos Santos, Ensenada, B. C., Mexico. The ovum fertilization of each species of sea urchin was estimated using a range of salinity from 33.4 to 53.4‰, being considered for each case its LC50. The results indicated that the capacity of fertilization of gametes decrease as the salinity increases, reaching the LC50 at 43.4‰ for Strongylocentrotus franciscanus and 48.4‰ for Lytechinus anamesus, confirming previous research that recommended not exceed 40‰ to avoid adverse effects in life cycles of the marine fauna.
The biological pump in the ocean plays an important role in the global carbon cycle. A substantia... more The biological pump in the ocean plays an important role in the global carbon cycle. A substantial portion of carbon is exported and preserved on continental margins, areas that support 10 to 15% of the total production of chlorophyll across the ocean with a contribution of more than 40% of the global organic carbon export to the ocean floor. Reconstruction of past primary productivity (PP) in areas of high biological activity is important to understand how climate change affects the global carbon cycle in different timescales. Burial rates of organic carbon (Corg) and biogenic opal (BSi) were measured in a core couplet GC31/PC08 from the Magdalena margin, SW of the peninsula of Baja California, in order to estimate changes in PP during the last 50,000 years. During the late Holocene (period between 3,000 years ago and today), the burial rate of BSi and Corg was lower than in the marine isotope stages 2 and 3 (occurred in the periods 29,000 to 14,000 and 57,000 to 29,000 years ago, ...
ABSTRACT The bulk sedimentary delta N-15 record of Alfonso Basin displayed changes both from a re... more ABSTRACT The bulk sedimentary delta N-15 record of Alfonso Basin displayed changes both from a regional source possibly associated with changes in the isotopic signal of NO3- dissolved in Subsurface Subtropical Water and from a climate source governed by solar forcing (total solar irradiance) over the strength of the North American monsoon (i.e., rainfall), causing intermediate water suboxia and promoting denitrification in the basin. High values of bulk sedimentary delta N-15 (maximum of 14.5%0) agree with increases in land-derived organic matter (from 14.8% to 49.2%) and with a decrease in terrigenous percentage (from 84.8% to 61.6%) during the Middle and Late Holocene, suggesting that increased rainfall and freshwater input promotes increased stratification of the water column, which inhibits vertical mixing and produces a reduction in oxygen content in an already oxygen-poor zone.
Sediment Transport Processes and Their Modelling Applications, 2013
ABSTRACT For sediment-transport models based on grain-size trend analysis there are consideration... more ABSTRACT For sediment-transport models based on grain-size trend analysis there are considerations that limit the inferences made about the net direction of the sediment transport. The most important limitation is the inability to validate the transport trends obtained with the hydrodynamic observations. We will use the LeRoux model to identify the dominant paths of sediment transport in Bahia Magdalena (upwelling subtropical system) and Bahia Chetumal (shallower tropical system). The grain-size trend was determined from 43 stations in Bahia Chetumal and 58 stations in Bahia Magdalena to identify the path of sediment transport. The analyses of principal components were used for the characteristics of the textural sediment in both studies. In Bahia Chetumal, the grain size and sorting explained at least 75% of the variance, with 20% of the variance explained by skewness. In Bahia Magdalena, the grain size and sorting explain 76% of the variance and skewness 22% of the variance. We established that the better-sorted sedimentary material is associated with stations with a fine grain-size and vice versa. The transport vectors suggest a net transport of sediment in the S-SE and S-SW directions, which is consistent with the direction of the surface and deep currents in Bahia Chetumal. The preferential deposition of fine and well-sorted material in the central part of the bay has an excellent correlation with the contents of anthropogenic pollutants found in other studies. The residual vectors of sediment transport in Bahia Magdalena suggest the presence of two gyres in the dispersion of the clastic material, a cyclonic-gyre in the central part and deeper portion and an anticyclonic-gyre in the southeast region of the bay. The pattern of sediment transport is consistent with the direction of the residual tidal currents in Bahia Magdalena. The contents of biogenic material found in this bay have an excellent correlation with the presence of these gyres and their preferential deposition.
Organic matter concentrations in a sediment core from the oxygen minimum zone (OMZ) off southern ... more Organic matter concentrations in a sediment core from the oxygen minimum zone (OMZ) off southern Baja California (705 m water depth) vary in concert with Dansgaard/Oeschger climate oscillations. A measure of sediment color (the third principal component of the diffuse ...
To monitor the composition and the vertical flux of particulate matter from the sea surface, a se... more To monitor the composition and the vertical flux of particulate matter from the sea surface, a sediment trap was moored in Cuenca Alfonso, Bahía de La Paz, a zone of high productivity in the southwestern Gulf of California. Carbonate-free samples from 2002 to 2005 were analyzed for C org, N, delta13C, and delta15N. The results show seasonal and interannual variability, with the delta13C and delta15N values larger in spring and summer than in fall and winter. The C:N ratio and delta13C increased by 1.5 units from 2002 to 2003-2005, suggesting a change in the supply of organic matter and-or the use or preferential degradation of N org. There was no interannual variation in delta15N. The occasional high delta15N values suggest that physical mechanisms, such as the shoaling and advection into the bay of 15N-rich subsurface equatorial water, occur over short time periods. The latter is presumed to be related to the periodic development of a significant cyclonic gyre in the southern Gulf.
The rates of accumulation of organic carbon, nitrogen and phosphorus (Corg, Norg, Porg), and of b... more The rates of accumulation of organic carbon, nitrogen and phosphorus (Corg, Norg, Porg), and of biogenic silica (BSi) were measured in sediment cores (GC31 and PC08) collected within the oxygen minimum zone of the Magdalena margin, off western Baja California Sur (Mexico). The rates of Corg, Norg and Porg accumulation were similar during marine isotopic stage 2 (MIS-2), the last glacial maximum (LGM) and the Late Holocene (LH, 3 kyrRecent), whereas the rate of BSi accumulation was greater during LGM and MIS-2 than during LH. In general, primary productivity during the MIS-2 and the LGM was similar to that observed during LH. The N/P ratio during the MIS-2 and the LGM was equivalent to that found during LH, suggesting that N and P were not limiting factors. In fact, the BSi/C ratio was relatively high (intense upwelling) when the N/P ratio was relatively low, indicating similar levels of primary productivity during the MIS-2, the LGM and LH. The results show that the productivity le...
The continental margin of the Northeast Pacific of Mexico (NEPM) is characterized by an oxygen mi... more The continental margin of the Northeast Pacific of Mexico (NEPM) is characterized by an oxygen minimum zone that allows the preservation and burial of organic carbon (Corg). In this work we evaluate the burial rate of sedimentary Corg of two cores (GC31 and PC08) collected from the Magdalena margin, Southern Baja California, Mexico. The flux of Corg in the Magdalena margin was compared with sedimentary records from the margins of Mazatlan and Gulf of Tehuantepec. The results indicate that the burial of Corg was larger during the Last Glacial maximum (LGM), of 800 mg/cm2/ka, and the Marine Isotope Stage-3 (MIS-3), of 900 mg/cm2/ka (with maximal values of 1400 mg/cm2/ka), than during the late Holocene (600 mg/cm2/ka), along the margin of the NEPM. These flux values of Corg indicate that the biological pump was 25 % more active during the LGM and 50% more efficient during the MIS-3 than during the late Holocene. The increase observed in the burial rates of Corg from low to mid latitude...
Hidrobiológica: [revista del Departamento de Hidrobiología]
The effects of increased salinity were evaluated on the ovum fertilization of the sea urchin spec... more The effects of increased salinity were evaluated on the ovum fertilization of the sea urchin species, Strongylocentrotus franciscanus Agassiz, 1863 and Lytechinus anamesus Clark, 1912, which were collected by means freediving in the bay Todos Santos, Ensenada, B. C., Mexico. The ovum fertilization of each species of sea urchin was estimated using a range of salinity from 33.4 to 53.4‰, being considered for each case its LC50. The results indicated that the capacity of fertilization of gametes decrease as the salinity increases, reaching the LC50 at 43.4‰ for Strongylocentrotus franciscanus and 48.4‰ for Lytechinus anamesus, confirming previous research that recommended not exceed 40‰ to avoid adverse effects in life cycles of the marine fauna.
The biological pump in the ocean plays an important role in the global carbon cycle. A substantia... more The biological pump in the ocean plays an important role in the global carbon cycle. A substantial portion of carbon is exported and preserved on continental margins, areas that support 10 to 15% of the total production of chlorophyll across the ocean with a contribution of more than 40% of the global organic carbon export to the ocean floor. Reconstruction of past primary productivity (PP) in areas of high biological activity is important to understand how climate change affects the global carbon cycle in different timescales. Burial rates of organic carbon (Corg) and biogenic opal (BSi) were measured in a core couplet GC31/PC08 from the Magdalena margin, SW of the peninsula of Baja California, in order to estimate changes in PP during the last 50,000 years. During the late Holocene (period between 3,000 years ago and today), the burial rate of BSi and Corg was lower than in the marine isotope stages 2 and 3 (occurred in the periods 29,000 to 14,000 and 57,000 to 29,000 years ago, ...
ABSTRACT The bulk sedimentary delta N-15 record of Alfonso Basin displayed changes both from a re... more ABSTRACT The bulk sedimentary delta N-15 record of Alfonso Basin displayed changes both from a regional source possibly associated with changes in the isotopic signal of NO3- dissolved in Subsurface Subtropical Water and from a climate source governed by solar forcing (total solar irradiance) over the strength of the North American monsoon (i.e., rainfall), causing intermediate water suboxia and promoting denitrification in the basin. High values of bulk sedimentary delta N-15 (maximum of 14.5%0) agree with increases in land-derived organic matter (from 14.8% to 49.2%) and with a decrease in terrigenous percentage (from 84.8% to 61.6%) during the Middle and Late Holocene, suggesting that increased rainfall and freshwater input promotes increased stratification of the water column, which inhibits vertical mixing and produces a reduction in oxygen content in an already oxygen-poor zone.
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