Marine Science Program & Earth and Ocean Sciences

Wetlands are well known to act as sinks for sediment and chemicals in the landscape. Within the Mkuze River floodplain in northern KwaZulu-Natal, South Africa, deposition of clastic sediment occurs predominantly in close proximity to the river channel, resulting in the formation of levees. Over time, this leads to channel avulsion, a process that may be accelerated by the activities of hippopotami whose trails create hydraulically favourable pathways. Sedimentation rates, determined using the isotopes 210 Pb and 137 Cs, indicate that the Mkuze River floodplain is a relatively rapidly aggrading system that should experience frequent avulsion, with average short-term rates in the order of 0.25 to 0.50 cm/y. Sediments on the floodplain are also an important sink for solutes, which concentrate in the groundwater and precipitate out because of evapotranspiration. Over long timescales, chemical sedimentation affects the landscape by influencing salinity, vegetation distribution, hydrological flows, and local topography. The Mkuze River floodplain is an actively evolving system, which continues to aggrade as a result of the combination of clastic and chemical sedimentation. In a region characterised by a strong annual water deficit, temporal patterns of clastic and chemical sedimentation are likely to exert influence on the long-term development of wetland systems elsewhere in southern Africa. This study, the first on sediment accretion rates using 210 Pb and 137 Cs dating for a southern African wetland, demonstrates that radioisotopic methods are an important tool that can be applied toward fully understanding wetland formation, evolution, and functioning in the region.

Direct measurements of new production and carbon export in the subtropical North Atlantic Ocean appear to be too low when compared to geochemical-based estimates. It has been hypothesized that episodic inputs of new nutrients into surface water via the passage of mesoscale eddies or winter storms may resolve at least some of this discrepancy. Here, we investigated particulate organic carbon (POC), particulate organic nitrogen (PON), and biogenic silica (BSiO 2 ) export using a combination of water column 234 Th: 238 U disequilibria and free-floating sediment traps during and immediately following two weather systems encountered in February and March 2004. While these storms resulted in a 2-4-fold increase in mixed layer NO 3 inventories, total chlorophyll a and an increase in diatom biomass, the systems were dominated by generally low 234 Th: 238 U disequilibria, suggesting limited particle export. Several 234 Th models were tested, with only those including non-steady state and vertical upwelling processes able to describe the observed 234 Th activities. Although upwelling velocities were not measured directly in this study, the 234 Th model suggests reasonable rates of 2.2-3.7 m d À1 .

Knowledge of temporal and spatial nutrient turnover and export rates is of great importance for a variety of investigations, ranging from nutrient limitation to contamination uptake and removal. However, there are few methods which allow for the in situ elucidation of these processes ...

Unusually high concentrations of the neurotoxin domoic acid (DA) were detected in a minke whale (Balaenoptera acutorostrata) carcass recovered during a severe harmful algal bloom (HAB), which occurred in southern California in April 2007. Cell fragments of the toxigenic diatom Pseudonitzschia australis were observed in whale gastric fluid and feces, corresponding to a dominance of Pseudo-nitzschia spp. in the phytoplankton community at the time of stranding. A high abundance of otoliths from a prominent DA vector, the northern anchovy (Engraulis mordax), were recovered in whale stomach contents, indicating trophic transfer of DA via the food web. Whale feces contained 258 µg DA per gram sample, exceeding DA concentrations reported for any marine mammal. DA intoxication was identified as the cause of mortality of this animal, expanding on the limited understanding of the impacts of DA-producing HABs on large whales.

Fog or cloud water (CW) deposition plays an important role in particle scavenging and the delivery of trace constituents to the Earth's surface. In this study, CW concentrations of total dissolvable iron (Fe) and aluminum (Al) were measured in 60 samples spanning 26 individual CW events throughout 1999 in Hawaii Volcanoes National Park on the island of Hawaii. Al concentrations ranged from 8 to 10,489 nM, with a median of 344 nM while Fe concentrations ranged from o 1 to 6419 nM with a median of 32 nM. CW deposition fluxes for Fe and Al ranged from 0.15-0.52 mmol Fe m À2 yr À1 and 0.62-1.35 mmol Al m À2 yr À1 , depending on the estimation method used. The large range in concentrations is higher than expected for a relatively pristine ecosystem. It appears that this inconsistency is due to emissions from the currently active nearby volcano, Kilauea. Categorizing CW events into volcanically versus less or non-volcanically impacted events suggests that although volcanically impacted events only accounted for 12% of fog water deposition, Kilauea Volcano was responsible at least 42% of the measured CW Al deposition and 61% of the CW Fe deposition measured for 1999. r

In this study, African red-rains were collected at Montseny (NE Spain) on a weekly basis and analyzed for total particulate phosphorus (TPP), total dissolved P (TDP) and soluble reactive P (SRP) for the period 1996e2008. Wet and dry weekly deposition of TPP was analyzed for all provenances in 2002e2003. In this period, African sources were found to contribute 66% of the 576 mmol m À2 y À1 of total particulate phosphorus (TPP) deposited in Montseny, split almost evenly between dry and wet deposition. Measurement of this dry deposition further allowed a direct determination of deposition velocity (V d ), which suggested significant depositional differences between African (V d ¼ 3.1 AE 0.80 cm s À1 ) and non-African events (V d ¼ 1.07 AE 0.13 cm s À1 ). Measurement of TDP concentrations during the African rains suggests a solubility of 11.2% TPP. SRP solubility was lower (2.2%), highlighting the importance of understanding the composition of the atmospherically derived P component. Samples were collected 25 km from the Mediterranean coast and were assumed to represent the atmospheric P input to coastal waters. On an annual basis, atmospheric-derived soluble P contributed <1% of annual new primary production in the western Mediterranean. However, one strong African dust event (22e27 May, 2008) accounted for 24e33 % of the atmospheric P-induced annual new production. These results highlight the potential biogeochemical importance of seasonality, source, and composition of aerosols deposited in the Western Mediterranean Sea.

ABSTRACT Excess nitrogen gas (excess N2) was measured in samples collected at six locations in the eastern and western sub-basins of the Cariaco Basin, Venezuela, in September 2008 (non-upwelling conditions) and March 2009 (upwelling conditions). During both sampling periods, excess N2 concentrations were below detection in surface waters, increasing to ~22 μmol N kg-1 at the oxic-anoxic interface ([O2] &amp;lt; ~ 4 μmol N kg-1, ~250 m). Below the oxic-anoxic interface (300-400 m), the average concentration of excess N2 was 24.7 ± 1.9 μmol N kg-1 in September 2008 and 27.5 ± 2.0 μmol N kg-1 in March 2009, i.e., excess N2 concentrations within this depth interval were ~ 3 μmol N kg-1 higher (p &amp;lt; 0.001) during the upwelling season compared to the non-upwelling period. These results suggest that N-loss in the Cariaco Basin may vary seasonally in response to changes in the flux of sinking particulate organic matter. We attribute the increase in excess N2 concentrations, or N-loss, observed during upwelling to: (1) higher availability of fixed nitrogen derived from suspended and sinking particles at the oxic-anoxic interface and/or (2) enhanced ventilation at the oxic-anoxic interface during upwelling.

234 Th, 228 Th and 210 Pb fluxes were measured in a series of sediment trap samples in Cariaco Basin from November 1995 to 8 May 1996. Sediment traps were located at 275, 455, 930 and 1255 m depth, with the 275 m trap just above the oxic/anoxic interface. Total mass, organic carbon, carbonate, biogenic opal, and lithogenic fluxes were also determined. Our results found that 234 Th, 228 Th and 210 Pb fluxes are highly correlated with total mass (r 2 ¼ 0:92 À 0:94), major sediment component fluxes (r 2 ¼ 0:82 À 0:93), and one another (r 2 ¼ 0:94 À 0:99). Decreases in radionuclide, total mass and major sediment component fluxes with depth were attributed to physical disaggregation and remineralization. While the 210 Pb specific activity loss from settling particles is the same as the bulk specific activity of the trapped particles between 455 and 930 m, the 210 Pb specific activity loss is substantially higher than the bulk specific activity of the trapped particles between 930 and 1255 m. We attributed this fractionation to a loss of minor components from settling particles. This suggests that minor components are responsible for the initial water column scavenging of 210 Pb in the Cariaco Basin. Steady state release of 210 Pb from settling particles would produce an anoxic water column activity an order of magnitude greater than previously reported. Therefore, a non-steady state removal mechanism must exist and is potentially caused by high sediment flux events from earthquake triggered turbidity currents or major plankton blooms. r (J.M. Smoak).

The naturally occurring radionuclides Th and Be were used to investigate the magnitude of upper ocean particulate organic carbon export and the rate of vertical eddy di!usion in the southwestern Gulf of Maine. Sampling occurred during the spring (March, April) and summer (July, August) of 1997. Both non-steady-state and horizontal transport models were assessed and found to be very important for the accurate determination of Th export. Upper ocean particulate organic carbon export was estimated using modeled Th export and the ratio of particulate organic carbon to Th on GF/F "lters. Our measurements demonstrate that the southwestern Gulf of Maine is typical of many coastal regimes, having an organic carbon export ratio (particulate export/primary production) which ranges from 9 to 49% depending on the depth of integration and primary productivity estimate. Be derived estimates of vertical eddy di!usivity into summer surface waters ranged from 0.5 to 1.5 cm sec\, and show that this mechanism is su$cient to support the amount of &new' nitrogen required for the measured particulate carbon export.

Export processes play a major role in regulating global marine primary production by reducing the efficiency of nutrient cycling and turnover in surface waters. Most studies of euphotic zone export focus on passive fluxes, that is, sinking particles. However, active transport, the vertical transfer of material by migrating zooplankton, can also be an important component of carbon (C) and nitrogen (N) removal from the surface ocean.

North Atlantic Ocean appear to be too low when compared to geochemical based estimates. It has been hypothesized that episodic inputs of new nutrients into surface water via the passage of mesoscale eddies or winter storms may resolve at least some of this discrepancy. Here, we investigated particulate organic carbon (POC), particulate organic nitrogen (PON), and biogenic silica (BSiO 2 ) export using a combination of water column 234 Th: 238 U disequilibria and free-floating sediment traps during and immediately following two weather systems encountered in February and March 2004. While these storms resulted in a 2-4 fold increase in mixed layer NO 3 inventories, total chlorophyll a and an increase in diatom biomass, the systems was dominated by generally low 234 Th: 238 U disequilibria, suggesting limited particle export. Several 234 Th models were tested, with only those including non-steady state and vertical upwelling processes able to describe the observed 234 Th activities. Although upwelling velocities were not measured directly in this study, the 234 Th model suggests reasonable rates of 2.2 to 3.7 m d -1 .

Ectohydrolase activities of suspended microbiota were compared to those associated with sinking particles (sed-POM) retrieved from sediment traps deployed in the permanently anoxic Cariaco Basin. In shore-based assays, activities of aminopeptidase, b-glucosidase, chitinase and alkaline phosphatase were measured in samples obtained from oxic and anoxic depths using MUF-and MCA-labeled fluorogenic substrate analogs. Hydrolysis potentials for these enzymes in the seston varied widely over the nine cruises sampled (8 Nov 1996-3 May 2000 and among depths (15-1265 m); from o10 to over 1600 nM d À1 hydrolysate released, generally co-varying with one another and with suspended particulate organic carbon (POC) and particulate nitrogen (PN). Hydrolytic potentials, prokaryotic abundances and POC/PN concentrations in sinking debris were 400-1.3 Â 10 7 times higher than in comparable volumes of seawater. However when normalized to PN, hydrolytic potentials in sediment trap samples were not demonstrably higher than in Niskin bottle samples. We estimate that PN pools in sediment trap samples were turned over 2-1400 times (medians ¼ 7-26x) slower by hydrolysis than were suspended PN pools. Median prokaryotic growth rates (divisions d À1 ) in sinking debris were also $150 times slower than for bacterioplankton. Hydrolytic potentials in surface oxic waters were generally faster than in underlying anoxic waters on a volumetric basis (nM hydrolysate d À1 ), but were not significantly (p40.05) different when normalized to PN or prokaryote abundances. Alkaline phosphatase was consistently the most active ectohydrolase in both sample types, suggesting that Cariaco Basin assemblages were adapted to decomposing phosphate esters in organic polymers. However, phosphorus limitation was not evident from nutrient inventories in the water column. Results support the hypothesis that efficiencies of polymer hydrolysis in anoxic waters are not inherently lower than in oxic waters.

Depth profiles of total 234 Th (dissolved+particulate) were collected at Station ALOHA (22145N, 158100W) in the North Pacific Subtropical Gyre during 9 cruises from April 1999 to March 2000. Samples were collected and processed by a new 2 L technique that enables more detailed depth resolution then previous 234 Th studies. Significant zones of particle export ( 234 Th deficiency) and particle remineralization ( 234 Th excess) were measured both temporally and with depth. 234 Th derived particulate carbon (PC) and nitrogen (PN) fluxes were determined with steady-state and non-steady-state models and PC/ 234 Th and PN/ 234 Th ratios measured with both in situ pumps and free-drifting particle interceptor traps deployed at 150 m. 234 Th based export estimates of 4.072.3 mmol C m À2 d À1 and 0.5370.19 mmol N m À2 d À1 , were approximately 60% higher than those measured in PIT style sediment traps from the same time period, 2.470.2 mmol C m À2 d À1 and 0.3270.08 mmol N m À2 d À1 . Most of this difference is attributable to two large export events that occurred during October and December 1999, when traps undercollected for 234 Th by a factor of 2 to 4. 234 Th export (ThE) ratios based on 234 Th derived PC flux/ 14 C based primary production ranged from 4% to 22% (average=8.8%). Our results confirm the recent estimates of C export by Emerson et al. (Nature 389 (1997) 951) and Sonnerup et al. (Deep-Sea Research I 46 (1999) 777) and indicate that C export from the oligotrophic ocean must be considered when discussing C sequestration in global climate change. r