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In addition to salinity and temperature, nutrient concentrations in surface waters are known to have a significant impact on distribution of carbonate-producing biota, but have never been quantitatively evaluated against different temperatures along a latitudinal transect. The western coast of the Gulf of California, Mexico, presents a natural laboratory for investigating the influence of oceanographic parameters such as salinity, temperature, and chlorophyll a, a proxy for nutrients, on the composition of a range of modern heterozoan and photozoan carbonate environments along a north-south latitudinal gradient spanning the entire warm-temperate realm (29degreesN-23degreesN). Chlorophyll a, measured in situ at half-hour resolution, is highly variable throughout the year due to short-term upwelling, and increases significantly from the southern to northern Gulf of California. Salinity, in contrast, fluctuates little and remains at an average of 35%. From south to north, carbonate production ranges from oligotrophic- mesotrophic, coral reefdominated shallow-water areas (minimum temperature 18.6 degreesC) through mesotrophic-eutrophic, red algal-dominated, inner-shelf carbonate production in the central gulf (minimum temperature 16 degreesC), and to molluscan-bryozoan, eutrophic inner- to outer-shelf environments (minimum temperature 13.7 degreesC). The Gulf of California data, supplemented with oceanographic and compositional information from a database compiled from a spectrum of modern carbonate systems worldwide, demonstrates the significance of nutrient control in the formation of heterozoan, photozoan, and transitional heterozoan-photozoan carbonate systems and serves as a basis for more accurately interpreting fossil carbonates
delta(18)O(benthic), values from Leg 194 Ocean Drilling Program Sites 1192 and 1195, (drilled on the Marion Plateau) were combined with deep-sea values to reconstruct the magnitude range of the late middle Miocene sea-level fall (13.6-11.4 Ma). In parallel, an estimate for the late middle Miocene sea-level fall was calculated from the stratigraphic relationship identified during Leg 194 and the structural relief of carbonate platforms that form the Marion Plateau. Corrections for thermal subsidence induced by Late Cretaceous rifting, flexural sediment loading, and sediment compaction were taken into account. The response of the lithosphere to sediment loading was considered for a range of effective elastic thicknesses (10 < T-e < 40 km). By overlapping the sea-level range of both the deep-sea isotopes and the results from the backstripping analysis, we demonstrate that the amplitude of the late middle Miocene sea-level fall was 45-68 m (56.5 +/- 11.5 m). Including an estimate for sea-level variation using the delta(18)O(benthic) results from the subtropical Marion Plateau, the range of sea-level fall is tightly constrained between 45 and 55 in (50.0 +/- 5.0 m). This result is the first precise quantitative estimate for the amplitude of the late middle Miocene eustatic fall that sidesteps the errors inherent in using benthic foraminifera assemblages to predict paleo-water depth. The estimate also includes an error analysis for the flexural response of the lithosphere to both water and sediment loads. Our result implies that the extent of ice buildup in the Miocene was larger than previously estimated, and conversely that the amount of cooling associated with this event was less important