E C I A L I S S U E O N C H A N G I N G O C E A N C H E M I S T R Y » A N T H R O P O C E N E : T H E F U T U R E … Sand ocean acidification. The article discusses the long-term changes in dissolved inorganic carbon (DIC), salinity-normalized DIC, and surface seawater pCO 2 (partial pressure of CO 2 ) due to the uptake of anthropogenic CO 2 and its impact on the ocean's buffering capacity. In addition, we evaluate changes in seawater chemistry that are due to ocean acidification and its impact on pH and saturation states for biogenic calcium carbonate minerals.

Over the last few decades, rising greenhouse gas emissions have promoted poleward expansion of the large-scale atmospheric Hadley circulation that dominates the Tropics, thereby affecting behavior of the Intertropical Convergence Zone (ITCZ) and North Atlantic Oscillation (NAO). Expression of these changes in tropical marine ecosystems is poorly understood because of sparse observational datasets. We link contemporary ecological changes in the southern Caribbean Sea to global climate change indices. Monthly observations from the CARIACO Ocean Time-Series between 1996 and 2010 document significant decadal scale trends, including a net sea surface temperature (SST) rise of ∼1.0 ± 0.14°C (±SE), intensified stratification, reduced delivery of upwelled nutrients to surface waters, and diminished phytoplankton bloom intensities evident as overall declines in chlorophyll a concentrations (ΔChla = −2.8 ± 0.5%·y −1 ) and net primary production (ΔNPP = −1.5 ± 0.3%·y −1 ). Additionally, phytoplankton taxon dominance shifted from diatoms, dinoflagellates, and coccolithophorids to smaller taxa after 2004, whereas mesozooplankton biomass increased and commercial landings of planktivorous sardines collapsed. Collectively, our results reveal an ecological state change in this planktonic system. The weakening trend in Trade Winds (−1.9 ± 0.3%·y −1 ) and dependent local variables are largely explained by trends in two climatic indices, namely the northward migration of the Azores High pressure center (descending branch of Hadley cell) by 1.12 ± 0.42°N latitude and the northeasterly progression of the ITCZ Atlantic centroid (ascending branch of Hadley cell), the March position of which shifted by about 800 km between 1996 and 2009. ecosystem state change | oceanography | plankton productivity P hytoplankton support over 95% of marine food webs and are responsible for about half of the Earth's conversion of CO 2 to biomass through net primary production (NPP) (1). Long-term declines in phytoplankton biomass and production in over 70% of the global ocean have been inferred recently from satellite imagery and century-long shipboard records of water clarity (2, 3). These reports of large-scale changes are at odds with trends directly observed at specific locations within the same ocean domains.

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GSA Data Repository item 2010032, study sites and sampling, geological setting of potential sedimentary inputs, chemical and interpretive methods, previous chemical work on Cariaco Basin surface sediments, and supporting tables and fi gures, is available online at www.geosociety.

TheCARIACO(Carbon Retention in a Colored Ocean) Ocean Time-Series Program station, located at 10.50°N, 64.66°W, observed biogeochemical and ecological processes in the Cariaco Basin of the southwestern Caribbean Sea from November 1995 to January 2017. The program completed 232 monthly core cruises, 40 sediment trap deployment cruises, and 40 microbiogeochemical process cruises. Upwelling along the southern Caribbean Sea occurs from approximately November to August. High biological productivity (320-628 g C m y) leads to large vertical fluxes of particulate organic matter, but only approximately 9-10 g C m y fall to the bottom sediments (∼1-3% of primary production). A diverse community of heterotrophic and chemoautotrophic microorganisms, viruses, and protozoa thrives within the oxic-anoxic interface. A decrease in upwelling intensity from approximately 2003 to 2013 and the simultaneous overfishing of sardines in the region led to diminished phytoplankton bloom intensities, increased phytoplankton diversity, and increased zooplankton densities. The deepest waters of the Cariaco Basin exhibited long-term positive trends in temperature, salinity, hydrogen sulfide, ammonia, phosphate, methane, and silica. Earthquakes and coastal flooding also resulted in the delivery of sediment to the seafloor. The program's legacy includes climate-quality data from suboxic and anoxic habitats and lasting relationships between international researchers. Expected final online publication date for the Annual Review of Marine Science Volume 11 is January 3, 2019. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earth–ocean–atmosphere dynamic exchange of elements. The ratios’ dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from ∼4.40 to 6.40 mmol:mol and ∼6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (∼4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (∼7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratios’ variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect.

Biometric characteristics of Orbulina universa (d'Orbigny) were used to differentiate two morphotypes present in sediment trap samples collected from the Cariaco Basin, Venezuela. Specifically, wall thickness and weight-area relationships were used to separate shells into thin (M thin ) and thick (M thick ) morphotypes. M thick (mean thickness = 19-41 μm) comprises 75% of the total O. universa in these samples and has morphometric characteristics similar to that of the previously described Type I Caribbean genotype, whereas M thin (mean thickness = 6-22 μm) is comparable to the Type III Mediterranean genotype. The flux of M thick increases during periods of upwelling, whereas M thin flux shows no systematic relationship with changing hydrographic regimes in the basin. The δ 18O and δ 13 C of M thick are on average 0.34‰ higher and 0.38‰ lower, respectively, than those of M thin , suggesting that they calcify their final spherical chamber at different depths in the water column and/or differ in their vital effects on shell geochemistry. Additionally, the absolute offset in the stable isotopic compositions of the two morphotypes varies as a function of surface ocean stratification. During periods of upwelling, the δ