Global Ocean Particulate Organic Carbon flux merged with satellite parameters

The efficiency of the biological pump of carbon to the deep ocean depends largely on the biologically mediated export of carbon from the surface ocean and its remineralization with depth. Global satellite studies have primarily focused on chlorophyll concentration and net primary production (NPP) to understand the role of phytoplankton in these processes. Recent satellite retrievals of phytoplankton composition now allow for the size of phytoplankton cells to be considered. Here, we improve understanding of phytoplankton size structure impacts on particle export, remineralization and transfer. Particulate organic carbon (POC) flux observations from sediment traps and 234Th are compiled across the global ocean. Annual climatologies of NPP, percent microplankton, and POC flux at four time series locations and within biogeochemical provinces are constructed, and sinking velocities are calculated to align surface variables with POC flux at depth. Parameters that characterize POC flux vs. depth (export flux ratio, labile fraction, remineralization length scale) are then fit to the aligned dataset. Times of the year dominated by different size compositions are identified and fit separately in regions of the ocean where phytoplankton cell size showed enough dynamic range over the annual cycle. Considering all data together, our findings support the paradigm of high export flux but low transfer efficiency in more productive regions and vice versa for oligotrophic regions. However, when parsing by dominant size class, we find periods dominated by small cells to have both greater export flux and lower transfer efficiency than periods when large cells comprise a greater proportion of the phytoplankton community.

Bryoliths constructed by bryozoans in symbiotic associations with hermit crabs, Golfe d'Arguin, Mauritania

The Golfe d'Arguin offshore of northern Mauritania hosts a rare modern analogue for heterozoan carbonate production in a tropical marine setting. Dominated by ocean upwelling and with additional fertilisation by iron-rich aeolian dust, this naturally eutrophic marine environment lacks typical photozoan communities. A highly productive, tropical cosmopolitan biota dominated by molluscs and suspension-feeders such as bryozoans and balanids characterises the carbonate-rich surface sediments. Overall biodiversity is relatively low and the species present are tolerant against the eutrophic and low-light conditions, the strong hydrodynamic regime governed by ocean upwelling, and the unstable, soft-bottom seafloor with few hard substrata. Here, we describe an ectosymbiosis between the hermit crab Pseudopagurus granulimanus (Miers, 1881) and monospecific assemblages of the encrusting cheilostome bryozoan Acanthodesia commensale (Kirkpatrick and Metzelaar, 1922) that cohabits vacant gastropod shells. Nucleating on an empty gastropod shell, the bryozoan colonies form multilamellar skeletal crusts that produce spherical encrustations and extend the living chamber of the hermit crab through helicospiral tubular growth. This non-obligate mutualistic symbiosis illustrates the adaptive capabilities and benefits from a close partnership in a complex marine environment, driven by trophic conditions, high water energies and instable substratum. Sectioned bryoliths show that between 49 and 97 % of the solid volume of the specimens consists of bryozoan skeleton.

Halocarbons (water) measured during Maria S. Merian cruise MSM18/3

Halocarbons from oceanic sources contribute to halogens in the troposphere, and can be transported into the stratosphere where they take part in ozone depletion. This paper presents distribution and sources in the equatorial Atlantic from June and July 2011 of the four compounds bromoform (CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I) and diiodomethane (CH2I2). Enhanced biological production during the Atlantic Cold Tongue (ACT) season, indicated by phytoplankton pigment concentrations, led to elevated concentrations of CHBr3 of up to 44.7 and up to 9.2 pmol/L for CH2Br2 in surface water, which is comparable to other tropical upwelling systems. While both compounds correlated very well with each other in the surface water, CH2Br2 was often more elevated in greater depth than CHBr3, which showed maxima in the vicinity of the deep chlorophyll maximum. The deeper maximum of CH2Br2 indicates an additional source in comparison to CHBr3 or a slower degradation of CH2Br2. Concentrations of CH3I of up to 12.8 pmol/L in the surface water were measured. In contrary to expectations of a predominantly photochemical source in the tropical ocean, its distribution was mostly in agreement with biological parameters, indicating a biological source. CH2I2 was very low in the near surface water with maximum concentrations of only 3.7 pmol/L. CH2I2 showed distinct maxima in deeper waters similar to CH2Br2. For the first time, diapycnal fluxes of the four halocarbons from the upper thermocline into and out of the mixed layer were determined. These fluxes were low in comparison to the halocarbon sea-to-air fluxes. This indicates that despite the observed maximum concentrations at depth, production in the surface mixed layer is the main oceanic source for all four compounds and one of the main driving factors of their emissions into the atmosphere in the ACT-region. The calculated production rates of the compounds in the mixed layer are 34 ± 65 pmol/m**3/h for CHBr3, 10 ± 12 pmol/m**3/h for CH2Br2, 21 ± 24 pmol/m**3/h for CH3I and 384 ± 318 pmol/m**3/h for CH2I2 determined from 13 depth profiles.

Composition of sediments from the Arabian Sea

Thirty seven deep-sea sediment cores from the Arabian Sea were studied geochemically (49 major and trace elements) for four time slices during the Holocene and the last glacial, and in one high sedimentation rate core (century scale resolution) to detect tracers of past variations in the intensity of the atmospheric monsoon circulation and its hydrographic expression in the ocean surface. This geochemical multi-tracer approach, coupled with additional information on the grain size composition of the clastic fraction, the bulk carbonate and biogenic opal contents makes it possible to characterize the sedimentological regime in detail. Sediments characterized by a specific elemental composition (enrichment) originated from the following sources: river suspensions from the Tapti and Narbada, draining the Indian Deccan traps (Ti, Sr); Indus sediments and dust from Rajasthan and Pakistan (Rb, Cs); dust from Iran and the Persian Gulf (Al, Cr); dust from central Arabia (Mg); dust from East Africa and the Red Sea (Zr/Hf, Ti/Al). Corg, Cd, Zn, Ba, Pb, U, and the HREE are associated with the intensity of upwelling in the western Arabian Sea, but only those patterns that are consistently reproduced by all of these elements can be directly linked with the intensity of the southwest monsoon. Relying on information from a single element can be misleading, as each element is affected by various other processes than upwelling intensity and nutrient content of surface water alone. The application of the geochemical multi-tracer approach indicates that the intensity of the southwest monsoon was low during the LGM, declined to a minimum from 15,000-13,000 14C year BP, intensified slightly at the end of this interval, was almost stable during the Bölling, Alleröd and the Younger Dryas, but then intensified in two abrupt successions at the end of the Younger Dryas (9900 14C year BP) and especially in a second event during the early Holocene (8800 14C year BP). Dust discharge by northwesterly winds from Arabia exhibited a similar evolution, but followed an opposite course: high during the LGM with two primary sources-the central Arabian desert and the dry Persian Gulf region. Dust discharge from both regions reached a pronounced maximum at 15,000-13,000 14C year. At the end of this interval, however, the dust plumes from the Persian Gulf area ceased dramatically, whereas dust discharge from central Arabia decreased only slightly. Dust discharge from East Africa and the Red Sea increased synchronously with the two major events of southwest monsoon intensification as recorded in the nutrient content of surface waters. In addition to the tracers of past dust flux and surface water nutrient content, the geochemical multi-tracer approach provides information on the history of deep sea ventilation (Mo, S), which was much lower during the last glacial maximum than during the Holocene. The multi-tracer approach-i.e. a few sedimentological parameters plus a set of geochemical tracers widely available from various multi-element analysis techniques-is a highly applicable technique for studying the complex sedimentation patterns of an ocean basin, and, specifically in the case of the Arabian Sea, can even reveal the seasonal structure of climate change.