Carbonates calibrated against oceanographic parameters along a latitudinal transect in the Gulf of California, Mexico

Abstract

Trophic resources are an important control governing carbonate production. Though this importance has long been recognized, no calibration exists to quantitatively compare biogenic assemblages within trophic resource fields. This study presents a field calibration of carbonate producers in a range of settings against high-resolution in situ measurements of nutrients, temperature and salinity. With its latitudinal extent from 30°to 23°N, the Gulf of California, Mexico, spans the warm-temperate realm and encompasses nutrient regimes from oligo-mesotrophic in the south to eutrophic in the north. Accordingly, from south to north carbonates are characterized by: (i) coral-dominated shallow carbonate factories (5-20 m water depth) with average sea-surface temperatures of 25°C (min. 18°C, max. 31°C), average salinities of 35AE06& and average chlorophyll a levels, which are a proxy for nutrients, of 0AE25 mg Chl a m )3 (max. 0AE48, min. 0AE1). (ii) Red algal-dominated subtidal to inner-shelf carbonate formation (10-25 m) in the central Gulf of California exhibiting average temperatures of 23°C (min. 18°C, max. 30°C), average salinities of 35AE25&, and average Chl a levels of 0AE71 Chl a m )3 (max. 5AE62, min. 0). (iii) Molluskan bryozoan-rich inner to outer shelf factories in the northern Gulf of California (20-50 m) with average sea surface temperatures of only 20°C (min. 13°C, max 29°C), average salinities of 35AE01&, and average contents of 2AE2 mg Chl a m )3 (max. 8AE38, min. 0). By calibrating sedimentological data with in situ measured oceanographic information in different environments, the response of carbonate producers to environmental parameters was established and extrapolated to carbonates on a global scale. The results demonstrate the importance of recognizing and quantifying trophic resources as a dominant control determining the biogenic composition and facies character of both modern and fossil carbonates.

Heterozoan carbonates in subtropical to tropical settings in the present and past

“…Accordingly, carbonate production ranges from coral-dominated shallow-water areas in the south to extensive rhodolith-dominated, inner shelf carbonate production in the central gulf, and to molluscan-bryozoan inner-to outer-shelf environments in the northern gulf ( Fig. 4b, c; Halfar et al 2006). With respect to modern rhodolith-dominated carbonates, the Gulf of California is one of the best-studied regions in the world (Steller and Foster 1995;Hetzinger et al 2006).…”

“…Located in a low-latitude setting (23°to 30°N), the Gulf of California is characterized by warm-temperate conditions (minimum monthly water temperatures in the south of 19°C and in the north 10°C; Alvarez-Borrego 1983) and encompasses nutrient regimes from oligo-mesotrophic in the south to eutrophic in the north (Alvarez-Borrego and Lara-Lara 1991; Halfar et al 2006). Along with increasing nutrients, depth of light penetration decreases.…”

“…For interpreting heterozoan carbonate deposits, it is crucial to separate the relative influence of different parameters such as temperature, trophic conditions and ocean chemistry, etc. (e.g., Pomar et al 2005;Halfar et al 2006). In the following, examples are presented that have been interpreted as tropical carbonates in spite of their heterozoan character, and the steering mechanisms for the biotic associations are discussed.…”

“…Generally, temperature and nutrient levels are anticorrelated in modern oceans (e.g., Halfar et al 2006). In settings with enhanced fluvial input, increased nutrient levels are generally accompanied by a decrease in salinities and an increase in sediment load.…”

“…One reason is that a concept of heterozoan and transitional photozoan-heterozoan (cf. Halfar et al 2006) carbonates in warm-water low-latitude settings has not yet been formally established. The aim of this paper is therefore to provide an overview of these heterozoan warm-water carbonates and the control mechanisms leading to their specific composition.…”