The rocky, photic benthos of Arctic and Subarctic Biogeographic Regions has a characteristic seaweed flora that includes an extensive high-magnesium calcium carbonate basal layer of crustose coralline red algae. The thickest (10-40 cm) and oldest parts of the crust (previously reported as up to 640-830 years old), primarily at mid-photic depths of 15-25 m, are composed of buildups of the genus Clathromorphum. Due to its annual growth increments and cycling of Mg content with temperature, Clathromorphum has recently been developed as a high-resolution climate archive. The age of the archive is primarily limited by the boring of mollusks that reduce structural integrity, remove the record, and induce local diagenesis. Depressions and gentle slopes in the deeper portions of Subarctic rocky bottoms often collect mixed bioclastic and siliciclastic sediments, including a dense cover of rhodoliths (Lithothamnion glaciale and Lithothamnion tophiforme). In this paper we describe a transition zone of these two environments that forms on cobble/boulder glacial erratic bottoms in northern Labrador. Clathromorphum compactum buildups on the boulders and cobbles projecting through rhodolith beds can be preserved by finegrained anaerobic sediments that in turn reduce mollusk boring. This significantly enhances preservation and longevity of C. compactum crusts. We describe specimens of ages up to 1200 years BP, and discuss how greater ages can be obtained for archiving high-resolution climate information.

Strongly influenced by seasonal and interannual (i.e. El Niño-Southern Oscillation) upwelling, the equatorial setting of the Gal apagos Archipelago is divided into well-defined temperature, nutrient and calcium carbonate saturation (Ω aragonite ) regions. To understand the relationship between oceanographic properties and sediment grain associations, grain size, carbonate content and components from sea floor surface samples were analysed, representing the main geographical regions of the Gal apagos Archipelago. The shallow-water rocky reefs of the Gal apagos Archipelago are characterized by mixed carbonate-siliciclastic slightly gravelly sands. Despite minor differences in carbonate content, major differences exist in the distribution and composition of key carbonate producing biota. Halimeda is absent and benthic foraminifera occur in extremely low abundance. The western side of the Gal apagos Archipelago is strongly influenced by nutrient-rich, low-Ω aragonite , subtropical water, which generates a heterozoan carbonate biofacies in a tropical realm resembling cold-water counterparts (i.e. serpulid, echinoderm, gastropod, barnacle and bryozoan-rich facies). The Central East region is composed of a transitional-heterozoan biofacies. Biofacies observed in the northern region have an increased occurrence of tropical corals, albeit with a minor overall contribution to the carbonate components. Although the temperature gradient would allow for a broader distribution of photozoan biofacies, the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories, mimicking cool-water, deeper or higher latitude environments. The recent sedimentary record of the Gal apagos Archipelago presents a range of tropical heterozoan carbonate communities, responding to more than simply latitude or temperature but a much more complex mixture of physical, evolutionary and geological processes.

The El Niño-Southern Oscillation (ENSO) is a periodic climatic and oceanic event caused by sea-surface temperature and nutrient anomalies over the eastern tropical Pacific Ocean (ETP). Recurring ENSO events have a significant impact on climate and the ecosystems of the circum-Pacific region. In the marine realm, ENSO is known for altering temperature and nutrient patterns, affecting the pelagic food chain, and causing widespread bleaching of corals due to temperature stress. The potential impacts of ENSO on shallow benthic ecosystems as a whole, however, are poorly understood. Here, we compared biogenic sedimentary facies of ETP shallow-water carbonate systems in a strongly ENSO-influenced area (Galápagos Islands, Ecuador [GAL]) with similar systems in an area less strongly influenced by ENSO (Gulf of California, Mexico [GOC]). Carbonate assemblages in both study regions range from coral-algal-dominated (photozoan) to molluscan-dominated (heterozoan) assemblages.Linear statistical models, comparing the distribution of carbonates against prominent local oceanographic parameters, show that minimum chlorophyll-a and maximum sea-surface temperature (which are both strongly influenced by ENSO) are dominant drivers shaping carbonate sediment facies in the GAL. In contrast, GOC carbonates have a distinct mean chlorophyll-a signature that is the result of an upwelling-induced north-south nutrient gradient not significantly influenced by ENSO.

In order to help predict the effects of anthropogenic stressors on shallow water carbonate environments, it is important to focus research on regions containing natural oceanographic gradients, particularly with respect to interactions between oceanography and ecologically sensitive carbonate producers. The Galápagos Archipelago, an island chain in the eastern equatorial Pacific, spans a natural nutrient, pH, and temperature gradient due to the interaction of several major ocean currents. Further, the region is heavily impacted by the El Niño—Southern Oscillation (ENSO) and the Galápagos exhibited widespread coral bleaching and degradation following the strong ENSO events of 1982–1983 and 1997–1998. These findings are coupled with reports of unusually low abundances of time-averaged benthic foraminiferal assemblages throughout the region. Foraminifera, shelled single-celled protists, are sensitive to environmental change and rapidly respond to alterations to their surrounding environment, making them ideal indicator species for the study of reef water quality and health. Here, statistical models and analyses were used to compare modern shallow water benthic foraminiferal assemblages from 19 samples spanning the Galápagos Archipelago to predominant oceanographic parameters at each collection site. Fisher α diversity indices, Ternary diagrams, Canonical Correspondence Analysis, regression tree analysis and FORAM-Index (FI; a single metric index for evaluating water quality associated with reef development) implied a combined impact from ENSO and upwelling from Equatorial Undercurrent (EUC) waters to primarily impact foraminiferal abundances and drive assemblage patterns throughout the archipelago. For instance, repeated ENSO temperature anomalies might be responsible for low foraminiferal density, while chronically high nutrients and low aragonite saturation and low pH—induced by EUC upwelling and La Niña anomalies—likely inhibited post-ENSO recovery, and caused foraminiferal assemblages to exhibit a heterotrophic dominance in the southern archipelago. What resulted are low FI values in the southern collection sites, indicating environments not conducive to endosymbiont development and/or recovery.