Dynamical Response of the Tropical Pacific Ocean to Solar Forcing During the Early Holocene

We present a high-resolution magnesium/calcium proxy record of Holocene sea surface temperature (SST) from off the west coast of Baja California Sur, Mexico, a region where interannual SST variability is dominated today by the influence of the El Nino-Southern Oscillation (ENSO). Temperatures were lowest during the early to middle Holocene, consistent with documented eastern equatorial Pacific cooling and numerical model simulations of orbital forcing into a La Nina-like state at that time. The early Holocene SSTs were also characterized by millennial-scale fluctuations that correlate with cosmogenic nuclide proxies of solar variability, with inferred solar minima corresponding to El Nino-like (warm) conditions, in apparent agreement with the theoretical "ocean dynamical thermostat" response of ENSO to exogenous radiative forcing

New constraints on deglacial marine radiocarbon anomalies from a depth transect near Baja California

Previous studies have shown that radiocarbon activities (C-14) in the low-latitude, middepth Pacific and Indian Oceans were anomalously low during Heinrich Stadial 1 (HS1, similar to 17.8-14.6ka) and the Younger Dryas (YD, similar to 12.8-11.5ka), coincident with intervals of rising atmospheric CO2 concentration and declining atmospheric C-14. However, a full explanation of these events remains elusive due to sparse and sometimes conflicting data. Here we present new C-14 measurements on benthic and planktic foraminifera that, in combination with previously published measurements, enable us to reconstruct the C-14 depth gradient near Baja California. Vertical profiles were similar to present during the Last Glacial Maximum and BOlling/Allerod (14.6-12.8ka) but display a pronounced middepth (similar to 700m) C-14 minimum during HS1 and the YD. The latter observation, along with a comparison to other regional reconstructions, appears to rule out intermediate waters from the north or from directly below as proximate sources of aged C-14-depleted ocean carbon during deglaciation and point instead to changes in the composition of Equatorial Pacific intermediate waters. Simple mixing constraints require Equatorial Pacific intermediate waters to be only slightly lower in C-14 than at Baja California, in contrast with previous observations of extremely low C-14 at Galapagos Rise. While the latter may have been influenced by localized releases of geologic (C-14-dead) CO2, the smaller and more widespread deglacial C-14 anomalies in the Arabian Sea and North Pacific seem to require a source of aged carbon in the glacial deep Southern and Pacific Oceans for which there is growing evidence

On the Preservation of Laminated Sediments Along the Western Margin of North America

[1] Piston, gravity, and multicores as well as hydrographic data were collected along the Pacific margin of Baja California to reconstruct past variations in the intensity of the oxygen-minimum zone (OMZ). Gravity cores collected from within the OMZ north of 24°N did not contain laminated surface sediments even though bottom water oxygen (BWO) concentrations were close to 5 μmol/kg. However, many of the cores collected south of 24°N did contain millimeter- to centimeter-scale, brown to black laminations in Holocene and older sediments but not in sediments deposited during the Last Glacial Maximum. In addition to the dark laminations, Holocene sediments in Soledad Basin, silled at 290 m, also contain white coccolith laminae that probably represent individual blooms. Two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated Holocene sediment occurring at 12.9 and 11.5 ka, respectively. The transition is delayed and more gradual (11.3–10.0 ka) in another dated core from Soledad Basin. The observations indicate that bottom-water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors. With the caveat that laminated sections should therefore not be correlated without independent age control, the pattern of older sequences of laminations along the North American western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr.</p

Correction: Coral Reef Health Indices versus the Biological, Ecological and Functional Diversity of Fish and Coral Assemblages in the Caribbean Sea.

[This corrects the article DOI: 10.1371/journal.pone.0161812.]

Coral Reef Health Indices <i>versus</i> the Biological, Ecological and Functional Diversity of Fish and Coral Assemblages in the Caribbean Sea

<div><p>This study evaluated the relationship between the indices known as the Reef Health Index (RHI) and two-dimensional Coral Health Index (2D-CHI) and different representative metrics of biological, ecological and functional diversity of fish and corals in 101 reef sites located across seven zones in the western Caribbean Sea. Species richness and average taxonomic distinctness were used to asses biological estimation; while ecological diversity was evaluated with the indices of Shannon diversity and Pielou´s evenness, as well as by taxonomic diversity and distinctness. Functional diversity considered the number of functional groups, the Shannon diversity and the functional Pielou´s evenness. According to the RHI, 57.15% of the zones were classified as presenting a "poor" health grade, while 42.85% were in "critical" grade. Based on the 2D-CHI, 28.5% of the zones were in "degraded" condition and 71.5% were "very degraded". Differences in fish and coral diversity among sites and zones were demonstrated using permutational ANOVAs. Differences between the two health indices (RHI and 2D-CHI) and some indices of biological, ecological and functional diversity of fish and corals were observed; however, only the RHI showed a correlation between the health grades and the species and functional group richness of fish at the scale of sites, and with the species and functional group richness and Shannon diversity of the fish assemblages at the scale of zones. None of the health indices were related to the metrics analyzed for the coral diversity. In general, our study suggests that the estimation of health indices should be complemented with classic community indices, or should at least include diversity indices of fish and corals, in order to improve the accuracy of the estimated health status of coral reefs in the western Caribbean Sea.</p></div

Three-way fully nested and permutational ANOVAs outcomes contrasting biological, ecological and functional diversity of reef fish among different health grades of the RHI and 2D-CHI indices, among zones nested in health grades and among sites nested in zones and health grades.

<p>Three-way fully nested and permutational ANOVAs outcomes contrasting biological, ecological and functional diversity of reef fish among different health grades of the RHI and 2D-CHI indices, among zones nested in health grades and among sites nested in zones and health grades.</p

Linear regression and Pearson correlation.

<p>a) species richness of fish, b) richness of functional groups of fish in relation to the grades of coral health, according to the RHI at the scale of sites. Dotted lines indicate the 95% confidence interval.</p

Grade of reef health estimated with the indices RHI and 2D-CHI in each study zone.

<p><b>a)</b> RHI health grade per zone; <b>b)</b> CHI health grade per zone.</p

Study area with zones of coral reefs in the western Caribbean.

<p>Cancún, Banco Chinchorro, Xcalak, Punta Manabique, Cayos Cochinos Media Luna, Cayos Miskitos.</p