Global Ocean Biomes: Mean and time-varying maps (NetCDF 7.8 MB)

Large-scale studies of ocean biogeochemistry and carbon cycling have often partitioned the ocean into regions along lines of latitude and longitude despite the fact that spatially more complex boundaries would be closer to the true biogeography of the ocean. Herein, we define 17 open-ocean biomes classified from four observational data sets: sea surface temperature (SST), spring/summer chlorophyll a concentrations (Chl a), ice fraction, and maximum mixed layer depth (maxMLD) on a 1° × 1° grid. By considering interannual variability for each input, we create dynamic ocean biome boundaries that shift annually between 1998 and 2010. Additionally we create a core biome map, which includes only the grid cells that do not change biome assignment across the 13 years of the time-varying biomes. These biomes can be used in future studies to distinguish large-scale ocean regions based on biogeochemical function.

Geochemical composition and atomic formulas of saponites, celadonites and carbonates from ODP Leg 168 sites

With this study, we investigate the mineralogical variations associated with the low-temperature (<100°C) alteration of normal tholeiitic pillow basalts varying in age from 0.8 to 3.5 Ma. Their alteration intensity varies systematically and is related to several factors, including (1) the aging of the igneous crust, (2) the increase of temperatures from the younger to the older sites, measured at the sediment/basement interface, (3) the local and regional variations in lithology and primary porosity, and (4) the degree of pillow fracturing. Fractures represent the most important pathways that allow significant penetration of fluids into the rock and are virtually the only factor controlling the alteration of the glassy rim and the early stages of pillow alteration. Three different alteration stages have been recognized: alteration of glassy margin, oxidizing alteration through fluid circulation in fracture systems, and reducing alteration through diffusion. All the observed mineralogical and chemical variations occurring during the early stages of alteration are interpreted as the result of the rock interaction with "normal," alkaline, and oxidizing seawater, along preferential pathways represented by the concentric and radial crack systems. The chemical composition of the fluid progressively evolves while moving into the basalt, leading to a reducing alteration stage, which is initially responsible for the precipitation of Fe-rich saponite and minor sulfides and subsequently for the widespread formation of carbonates. At the same time, the system evolved from being "water dominated" to being "rock dominated." No alteration effects in pillow basalts were observed that must have occurred at temperatures higher than those measured during Leg 168 at the basement/sediment interface (e.g., between 15° and 64°C).

Holocene sedimentation rates in the Northwest Passage

Palynological, geochemical, and physical records were used to document Holocene paleoceanographic changes in marine sediment core from Dease Strait in the western part of the main axis of the Northwest Passage (core 2005-804-006 PC latitude 68°59.552'N, longitude 106°34.413'W). Quantitative estimates of past sea surface conditions were inferred from the modern analog technique applied to dinoflagellate cyst assemblages. The chronology of core 2005-804-006 PC is based on a combined use of the paleomagnetic secular variation records and the CALS7K.2 time-varying spherical harmonic model of the geomagnetic field. The age-depth model indicates that the core spans the last ~7700 cal years B.P., with a sedimentation rate of 61 cm/ka. The reconstructed sea surface parameters were compared with those from Barrow Strait and Lancaster Sound (cores 2005-804-004 PC and 2004-804-009 PC, respectively), which allowed us to draw a millennial-scale Holocene sea ice history along the main axis of the Northwest Passage (MANWP). Overall, our data are in good agreement with previous studies based on bowhead whale remains. However, dinoflagellate sea surface based reconstructions suggest several new features. The presence of dinoflagellate cysts in the three cores for most of the Holocene indicates that the MANWP was partially ice-free over the last 10,000 years. This suggests that the recent warming observed in the MANWP could be part of the natural climate variability at the millennial time scale, whereas anthropogenic forcing could have accelerated the warming over the past decades. We associate Holocene climate variability in the MANWP with a large-scale atmospheric pattern, such as the Arctic Oscillation, which may have operated since the early Holocene. In addition to a large-scale pattern, more local conditions such as coastal current, tidal effects, or ice cap proximity may have played a role on the regional sea ice cover. These findings highlight the need to further develop regional investigations in the Arctic to provide realistic boundary conditions for climatic simulations.

(Table 1) Chlorophyll a content and microalgae abundance and biovolume in pack ice in the Bellingshausen Sea

Pack ice in the Bellingshausen Sea contained moderate to high stocks of microalgal biomass (3-10 mg Chl a/m**2) spanning the range of general sea-ice microalgal microhabitats (e.g., bottom, interior and surface) during the International Polar Year (IPY) Sea Ice Mass Balance in the Antarctic (SIMBA) studies. Measurements of irradiance above and beneath the ice as well as optical properties of the microalgae therein demonstrated that absorption of photosynthetically active radiation (PAR) by particulates (microalgae and detritus) had a substantial influence on attenuation of PAR and irradiance transmission in areas with moderate snow covers (0.2-0.3 m) and more moderate effects in areas with low snow cover. Particulates contributed an estimated 25 to 90% of the attenuation coefficients for the first-year sea ice at wavelengths less than 500 nm. Strong ultraviolet radiation (UVR) absorption by particulates was prevalent in the ice habitats where solar radiation was highest - with absorption coefficients by ice algae often being as large as that of the sea ice. Strong UVR-absorption features were associated with an abundance of dinoflagellates and a general lack of diatoms - perhaps suggesting UVR may be influencing the structure of some parts of the sea-ice microbial communities in the pack ice during spring. We also evaluated the time-varying changes in the spectra of under-ice irradiances in the austral spring and showed dynamics associated with changes that could be attributed to coupled changes in the ice thickness (mass balance) and microalgal biomass. All results are indicative of radiation-induced changes in the absorption properties of the pack ice and highlight the non-linear, time-varying, biophysical interactions operating within the Antarctic pack ice ecosystem.

Minerals and geochemistry abundance and occurance, as well as K-Ar determinations for DSDP Site 92-597 basalts

Preliminary studies of hydrothermally altered massive basalts formed at the fast-spreading Mendoza Rise and recovered from DSDP Holes 597B and 597C indicate the presence of three secondary mineral assemblages which formed in the following order: (1) trioctahedral chlorite and talc, (2) goethite and smectite, and (3) calcite and celadonite. The sequential precipitation of these mineral assemblages denotes high water:rock ratios and time-varying conditions of temperature (early >200°C to late <30°C) and state of oxidation (early nonoxidative to late oxidative). A decrease in the relative proportion of oxidative mineral assemblages with depth to 70 m in Site 597 basement indicates a zone of oxidative alteration that became shallower with time as the deeper, more constricted fracture systems were filled by secondary mineralization. In this report we present the first results of the K-Ar dating of celadonite formation age; celadonite formation reflects end-stage hydrothermal alteration in Site 597 basement. Three celadonite dates obtained from Site 597 samples include 13.1 ± 0.3 m.y. from 17 m basement depth (Hole 597B), 19.9 ± 0.4 m.y. from 18 m basement depth (Hole 597C), and 19.3 ± 1.6 m.y. from 60 m basement depth (Hole 597C). The age of host rock crystallization (28.6 m.y.) and the K-Ar dates of celadonite formation establish that hydrothermal alteration in the upper 70 m of Site 597 basement continued for at least 10 m.y. and possibly as long as 16 m.y. after basalt crystallization at the ridge crest. Assuming a half-spreading rate of 55 km/m.y., we calculate that hydrothermal circulation was active in shallow basement at a distance of at least 550 km off ridge crest and possibly as far as 1000 km off ridge crest.