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1.
In order to estimate the contribution of cold Pacific deep water to the Indonesian throughflow (ITF) and the flushing of the deep Banda Sea, a current meter mooring has been deployed for nearly 3 years on the sill in the Lifamatola Passage as part of the International Nusantara Stratification and Transport (INSTANT) programme. The velocity, temperature, and salinity data, obtained from the mooring, reflect vigorous horizontal and vertical motion in the lowest 500 m over the ～2000 m deep sill, with speeds regularly surpassing 100 cm/s. The strong residual flow over the sill in the passage and internal, mainly diurnal, tides contribute to this bottom intensified motion. The average volume transport of the deep throughflow from the Maluku Sea to the Seram Sea below 1250 m is 2.5 Sv (1 Sv=106 m3/s), with a transport-weighted mean temperature of 3.2 °C. This result considerably increases existing estimates of the inflow of the ITF into the Indonesian seas by about 25% and lowers the total mean inflow temperature of the ITF to below 13 °C. At shallower levels, between 1250 m and the sea surface, the flow is directed towards the Maluku Sea, north of the passage. The typical residual velocities in this layer are low (～3 cm/s), contributing to an estimated northward flow of 0.9–1.3 Sv. When more results from the INSTANT programme for the other Indonesian passages become available, a strongly improved estimate of the mass and heat budget of the ITF becomes feasible.  相似文献   

2.
Sea-ice and water samples were collected at 14 stations on the shelves and slope regions of the Chukchi and Beaufort Seas during the spring 2002 expedition as part of the Shelf–Basin Interaction Studies. Algal pigment content, particulate organic carbon and nitrogen, and primary productivity were estimated for both habitats based on ice cores, brine collection and water samples from 5-m depth. The pigment content (0.2–304.3 mg pigments m−2) and primary productivity (0.1–23.0 mg C m−3 h−1) of the sea-ice algae significantly exceeded water-column parameters (0.2 and 1.0 mg pigments m−3; <0.1–0.4 mg C m−3 h−1), making sea ice the habitat with the highest food availability for herbivores in early spring in the Chukchi and Beaufort Seas. Stable isotope signatures for ice and water samples did not differ significantly for δ15N, but for δ13C (ice: −25.1‰ to −14.2‰; water: −26.1‰ to −22.4‰). The analysis of nutrient concentrations and the pulse-amplitude-modulated fluorescence signal of ice algae and phytoplankton indicate that nutrients were the prime limiting factor for sea-ice algal productivity. The estimated spring primary production of about 1–2 g C m−2 of sea-ice algae on the shelves requires the use of substantial nutrient reservoirs from the water column.  相似文献   

3.
The realization of North Atlantic Deep Water (NADW) replacement in the deep northern Indian Ocean is crucial to the “conveyor belt” scheme. This was investigated with the updated 1994 Levitus climatological atlas. The study was performed on four selected neutral surfaces, encompassing the Indian deep water from 2000 to 3500 m. The Indian deep water comprises three major water masses: NADW, Circumpolar Deep Water (CDW) and North Indian Deep Water (NIDW). Since NADW flowing into the southwest Indian Ocean is largely blocked by the ridges (the Madagascar Ridge in the east and Davie Ridge in the north in the Mozambique Channel) and NIDW is the only source in the northern Indian Ocean that cannot provide a large amount of volume transport, CDW has to be a major source for the Indian deep circulation and ventilation in the north. Thus the question of NADW replacement becomes that of how the advective flows of CDW from the south are changed to be upwelled flows in the north—a water-mass transformation scenario. This study considered various processes causing motion across neutral surfaces. It is found that dianeutral mixing is vital to achieve CDW transformation. Basin-wide uniform dianeutral upwelling is detected in the entire Indian deep water north of 32°S, somewhat concentrated in the eastern Indian Ocean on the lowest surface. However, the integrated dianeutral transport is quite low, about a net of 0.2 Sv (1 Sv=106 m3 s-1) across the lowermost neutral surface upward and 0.4 Sv across the uppermost surface upward north of 32°S with an error band of about 10–20% when an uncertainty of half-order change in diffusivities is assumed. Given about 10–15% of rough ridge area where dianeutral diffusivity could be about one order of magnitude higher (10-4 m2 s-1) due to internal-wave breaking, the additional amount of increased net dianeutral transport across the lowest neutral surface is still within that error band. The averaged net upward transport in the north is matched with a net downward transport of 0.3 Sv integrated in the Southern Ocean south of 45°S across the lowermost surface. With the previous works of You (1996. Deep Sea Research 43, 291–320) in the thermocline and You (Journal of Geophysical Research) in the intermediate water combined, a schematic dianeutral circulation of the Indian Ocean emerges. The integrated net dianeutral upwelling transport shows a steady increase from the deep water to the upper thermocline (from 0.2 to 4.6) north of 32°S. The dianeutral upwelling transport is accumulated upward as the northward advective transport provided from the Southern Ocean increases. As a result, the dianeutral upwelling transport north of 32°S can provide at least 4.6 Sv to south of 32°S from the upper main thermocline, most likely to the Agulhas Current system. This amount of dianeutral upwelling transport does not include the top 150–200 m, which may contribute much more volume transport to the south.  相似文献   

4.
For the first time in situ, deep penetrating O2 profiles were measured in abyssal sediments in the western South Atlantic. Construction of deep penetrating O2 optodes and adaptation to a benthic profiling lander are described. The opto-chemical oxygen sensors allow measurements to a depth of 55 cm in marine sediments. A vertical resolution of 0.5 cm was used to determine the O2 dynamics in those oligotrophic deep sea sediments; the oxygen concentration across the sediment water interface was measured with a resolution of 100 μm. Oxygen penetration depth (OPD), diffusive oxygen uptake (DOU) and oxygen consumption rates were determined at four stations north of the Amazon fan and one at the Mid-Atlantic Ridge. Diffusive oxygen uptake rates ranged from 0.1 to 0.9 mmol m−2 d−1; the oxygen penetration depth ranged from 8 to 26 cm. Carbon consumption rates calculated from the diffusive oxygen uptake rates were in the range of 0.3–3.0 g C m−2 a−1. Comparison between in situ and laboratory DOU and OPD measurements confirmed previous findings that core recovery and warming have strong effects on the oxygen dynamics in deep sea sediments. Laboratory measurements yielded a decrease of 50–75% in OPD and consequently an increase in DOU by 1.5 and 18-times. Deep penetrating oxygen optodes provide a new tool to accurately determine oxygen dynamics (and thereby calculate carbon mineralization rates) in oligotrophic sediments. However, oxygen optodes as used in this study do not resolve the diffusive boundary layer (DBL). The data show that deep penetrating O2 optodes in combination with high-resolution O2 microelectrodes give a complete picture of the oxygen dynamics, including the DBL, in deep sea sediments.  相似文献   

5.
Sulfate reduction rate measurements by the 35SO42− core injection method were carried out in situ with a benthic lander, LUISE, and in parallel by shipboard incubations in sediments of the Black Sea. Eight stations were studied along a transect from the Romanian shelf to the deep western anoxic basin. The highest rates measured on an areal basis for the upper 0–15 cm were 1.97 mmol m−2 d−1 on the shelf and 1.54 mmol m−2 d−1 at 181 m water depth just below the chemocline. At all stations sulfate reduction rates decreased to values <3 nmol cm−3 d−1 below 15 cm depth in the sediment. The importance of sulfate reduction relative to the total mineralization of organic matter was very low, 6%, on the inner shelf, which was paved with mussels, and increased to 47% on the outer shelf at 100 m depth. Where the oxic–anoxic interface of the water column impinged on the sea floor at around 150 m depth, the contribution of sulfate reduction increased from >50% just above the chemocline to 100% just below. In the deep sea, mean sulfate reduction rates were 0.6 mmol m−2 d−1 corresponding to an organic carbon oxidation of 1.3 mmol m−2 d−1. This is close to the mean sedimentation rate of organic carbon over the year in the western basin. A comparison with published data on sulfate reduction in Black Sea sediments showed that the present results tend to be higher in shelf sediments and lower in the deep-sea than most other data. Based on the present water column H2S inventory and the H2S flux out of the sediment, the calculated turnover time of H2S below the chemocline is 2100 years.  相似文献   

6.
Seven years (2001–2008) of dissolved organic carbon (DOC) vertical profiles were examined in order to assess the main processes determining DOC concentration and distribution in the meso- and bathypelagic layers of the Mediterranean Sea. As expected, DOC showed high and highly variable concentrations in the surface layer of 57–68 μM (average values between 0 and 100 m), with a decrease to 44–53 μM between 200 and 500 m. Deep DOC distribution was strongly affected by deep-water formation, with a significant increase to values of 76 μM in recently ventilated deep waters, and low concentrations, comparable to those observed in the open oceanic waters (34–45 μM), where the oldest, deep waters occurred. In winter 2004/2005 a deep-water formation event was observed and the consequent DOC export at depth was estimated to range between 0.76–3.02 Tg C month–1. In the intermediate layer, the main path of the Levantine Intermediate Water (LIW) was followed in order to estimate the DOC consumption rate in its core. Multiple regression between DOC, apparent oxygen utilization (AOU), and salinity indicated that 38% of the oxygen consumption was related to DOC mineralization when the effect of mixing was removed. In deep waters of the southern Adriatic Sea a DOC decrease of 6 μM, together with an AOU increase of 9 μM, was observed between the end of January 2008 and the end of June 2008 (5 months). These data indicate a rate of microbial utilization of DOC of about 1.2 μM C month−1, with 92% of the oxygen consumption due to DOC mineralization. These values are surprisingly high for the deep sea and represent a peculiarity of the Mediterranean Sea.  相似文献   

7.
In this study we estimate diffusive nutrient fluxes in the northern region of Cape Ghir upwelling system (Northwest Africa) during autumn 2010. The contribution of two co-existing vertical mixing processes (turbulence and salt fingers) is estimated through micro- and fine-structure scale observations. The boundary between coastal upwelling and open ocean waters becomes apparent when nitrate is used as a tracer. Below the mixed layer (56.15±15.56 m), the water column is favorable to the occurrence of a salt finger regime. Vertical eddy diffusivity for salt (Ks) at the reference layer (57.86±8.51 m, CI 95%) was 3×10−5 (±1.89×10−9, CI 95%) m2 s−1. Average diapycnal fluxes indicate that there was a deficit in phosphate supply to the surface layer (6.61×10−4 mmol m−2 d−1), while these fluxes were 0.09 and 0.03 mmol m−2 d−1 for nitrate and silicate, respectively. There is a need to conduct more studies to obtain accurate estimations of vertical eddy diffusivity and nutrient supply in complex transitional zones, like Cape Ghir. This will provide us with information about salt and nutrients exchange in onshore–offshore zones.  相似文献   

8.
The vertical distribution (0–900 m) of zooplankton biomass and indices of feeding (gut fluorescence, GF) and metabolism (electron transfer system, ETS) were studied across an anticyclonic eddy south of Gran Canaria Island (Canary Islands). Two dense layers of organisms were clearly observed during the day, one above 200 m and the other at about 500 m, coincident with the deep scattering layer (DSL). The biomass displacement due to interzonal migrants in the euphotic zone was more than 2-fold higher than that previously reported for the southern area of this archipelago. The gut flux estimated (0.14–0.44 mgC m−2 d−1) was similar to the values previously found in the Canaries. The respiratory flux outside the eddy (1.85 mgC m−2 d−1) was in the lower range of values reported for this area. Inside the eddy, migrant biomass and respiration rates were 2- and 4- fold higher than in the surrounding waters. Active flux mediated by diel vertical migrants inside the eddy (8.28 mgC m−2 d−1) was up to 53% of the passive carbon flux to the mesopelagic zone (15.8 mgC m−2 d−1). It is, therefore, suggested that the anticyclonic eddy enhanced both migration from deep waters and active flux.  相似文献   

9.
Using bifrequency sonar (38 kHz, 120 kHz) directed towards the open sea from the inside of a submarine cave, two species of Mysidacea (Crustacea), similar in shape but not in size, and with different patterns of behaviour, were observed simultaneously and discriminated, and their biomass was estimated during their migration. The first species, Hemimysis speluncola (<1 cm length), lives in the submarine cave, forming a distinct community that migrates horizontally. The second species, Siriella jaltensis (>1 cm length), lives in the open sea and migrates vertically. These species are both detected clearly at 120 kHz, but only the larger one, Siriella jaltensis, is detected at 38 kHz. This distinction allows one to determine the size limits of planktonic objects detected at these frequencies, i.e. 3 mm at 120 kHz and 10 mm at 38 kHz, corresponding to one quarter of the wavelength. The target strength (TS) of each species was calculated from the field data and compared to results calculated from three models. As the volume of the cave occupied by the Hemimysis population is about 300 m3, and the density of the swarm is 36,000 individuals/m3, the number of individuals in the cave is estimated to be around 10 million (or 24 kg). The density of the open-water population of Siriella is estimated to be 13 individuals/m3.  相似文献   

10.
The mesoscale dynamics of the Scottish side of the Faroe–Shetland Channel have been investigated using synoptic in situ and remote sensing observations. A cold core cyclonic eddy, identified from an AVHRR image, had a diameter of about 50 km and surface current speeds of up to 50 cm s-1; it appeared to be attached to the 800 m isobath as it moved north-eastward along the edge of the channel at about 8 cm s-1. Speeds in the slope current were about 50 cm s-1 but increased to 70 cm s-1 where the current was compressed by the eddy. Offshore, over the 1000 m isobath in the cooler water, speeds in the current were slower (ca. 20 cm s-1). North-west of the Shetlands the offshore edge of the slope current was deflected across the channel for a distance of about 70 km from the shelf edge. The speed of drifters in the slope current increased to over 60 cm s-1 as they moved anti-cyclonically around this deflection. CTD profiles suggest that the movement of the surface waters was mirrored in the deep water of the channel. The deflection carried a very large quantity of North Atlantic Water into the central part of the channel; its cause and ultimate fate are not known, although it is likely to have had a significant impact on the dynamics of the channel.  相似文献   

11.
A novel autonomous free-fall lander vehicle, with a capability down to 6000 m, was deployed off Cape Verde for studies on bioluminescence in the deep sea. The system was equipped with a high-sensitivity Intensified Silicon Intensified Target (ISIT) video camera, a programmable control-recording unit and an acoustic current meter with depth and temperature sensors. The ISIT lander was used in three modes: (1) free falling at 34 m min−1, with the camera looking downwards at a mesh screen, recording impacts of luminescent organisms to obtain a vertical profile down to the abyssal sea floor, sampling at >100 l s−1; (2) rotating, with the lander on the sea floor and the camera orienting to the bottom current using a servo-controlled turntable, impacts of luminescent organisms carried by the bottom current onto a mesh screen mounted 0.5 m in front of the camera were recorded to estimate abundance in the benthic boundary layer; (3) baited, with the camera focused on a bait placed on the sea floor.Profiles recorded abundance of luminescent organisms as 26.7 m−3 at 500–999 m depth, decreasing to 1.6 m−3 at 2000–2499 m and 0.5 m−3 between 2500 m and the sea floor at 4046 m, with no further detectable significant change with depth. Rotator measurements at a 0.5 m height above the sea floor gave a mean abundance of 0.47 m−3 in the benthic boundary layer at 4046 m and of 2.04 m−3 at 3200 m. Thirty five minutes after the bait was placed on the sea floor at 3200 m, bioluminescent fauna apparently arrived at the bait and produced luminescent displays at a rate of 2 min−1. Moving, flashing light sources were observed and luminescent material was released into the bottom current.  相似文献   

12.
Between 2 and 3 km depth, North Pacific deep waters contain a plume of water with high silicic acid concentrations. The plume extends outward from Cascadia Basin (the Washington Margin), where waters can contain in excess of 200 μM off the coast of Oregon and Washington. To identify the source of the high Si concentrations in Cascadia Basin, we measured silicic acid and germanium concentrations in deep waters, and their fluxes from sediments using incubated cores. The mean flux of silicic acid into bottom waters is 0.81±0.05 mmol/m2-day, and the Ge/Si ratio of this flux is 0.7±0.1 μmol/mol. A box model, incorporating these results with hydrographic data, indicates that (1) no more than 5% of the silicic acid added to Basin deep waters can have a hydrothermal source (either hot or warm seeps), and (2) the total input of silicic acid to Basin deep waters is 0.06±0.02 Tmol/y. This input is nearly all from remineralized biogenic debris and should contribute about 0.5% of the 14 Tmol/y that are estimated to be necessary to maintain the North Pacific plume.  相似文献   

13.
The Arctic Ocean has wide shelf areas with extensive biological activity including a high primary productivity and an active microbial loop within the surface sediment. This in combination with brine production during sea ice formation result in the decay products exiting from the shelf into the deep basin typically at a depth of about 150 m and over a wide salinity range centered around S ～33. We present data from the Beringia cruise in 2005 along a section in the Canada Basin from the continental margin north of Alaska towards the north and from the International Siberian Shelf Study in 2008 (ISSS-08) to illustrate the impact of these processes. The water rich in decay products, nutrients and dissolved inorganic carbon (DIC), exits the shelf not only from the Chukchi Sea, as has been shown earlier, but also from the East Siberian Sea. The excess of DIC found in the Canada Basin in a depth range of about 50–250 m amounts to 90±40 g C m?2. If this excess is integrated over the whole Canadian Basin the excess equals 320±140×1012 g C. The high DIC concentration layer also has low pH and consequently a low degree of calcium carbonate saturation, with minimum aragonite values of 60% saturation and calcite values just below saturation. The mean age of the waters in the top 300 m was calculated using the transit time distribution method. By applying a future exponential increase of atmospheric CO2 the invasion of anthropogenic carbon into these waters will result in an under-saturated surface water with respect to aragonite by the year 2050, even without any freshening caused by melting sea ice or increased river discharge.  相似文献   

14.
Highly sensitive STOX O2 sensors were used for determination of in situ O2 distribution in the eastern tropical north and south Pacific oxygen minimum zones (ETN/SP OMZs), as well as for laboratory determination of O2 uptake rates of water masses at various depths within these OMZs. Oxygen was generally below the detection limit (few nmol L−1) in the core of both OMZs, suggesting the presence of vast volumes of functionally anoxic waters in the eastern Pacific Ocean. Oxygen was often not detectable in the deep secondary chlorophyll maximum found at some locations, but other secondary maxima contained up to ~0.4 µmol L−1. Directly measured respiration rates were high in surface and subsurface oxic layers of the coastal waters, reaching values up to 85 nmol L−1 O2 h−1. Substantially lower values were found at the depths of the upper oxycline, where values varied from 2 to 33 nmol L−1 O2 h−1. Where secondary chlorophyll maxima were found the rates were higher than in the oxic water just above. Incubation times longer than 20 h, in the all-glass containers, resulted in highly increased respiration rates. Addition of amino acids to the water from the upper oxycline did not lead to a significant initial rise in respiration rate within the first 20 h, indicating that the measurement of respiration rates in oligotrophic Ocean water may not be severely affected by low levels of organic contamination during sampling. Our measurements indicate that aerobic metabolism proceeds efficiently at extremely low oxygen concentrations with apparent half-saturation concentrations (Km values) ranging from about 10 to about 200 nmol L−1.  相似文献   

15.
The geographical distribution of barotropic to baroclinic transfer of tidal energy by baroclinic wave drag in the abyssal ocean is estimated. Using tidal velocities from a state-of-the-art numerical tidal model, the total loss of barotropic tidal energy in the deep ocean (between 70°S and 70°N and at depths greater than 1000 m) is estimated to be about 0.7 TW (M2) corresponding to a mean value of the energy flux (e) of 2.4×10−3 W/m2. The distribution of e is however highly skewed with a median of about 10−6 W/m2. Only 10% of the area is responsible for more than 97% of the total energy transfer.To assess the possible influence of the relatively coarse bathymetry representation upon the present estimate, complementary calculations using better resolved sea floor topography are carried out over a control area around the Hawaiian Ridge. There are no major differences between the results achieved using the two different bathymetry databases. Fluxes of about 16 GW or 6×10−3 W/m2 are computed in both cases, and the main contributions to the total fluxes originate in the same range of e-values and cover equally large parts of the total area.It is not clear whether the present model is valid at flat or subcritical bottom slopes. However, for the Hawaiian region, only 2% of the total energy flux as calculated in the present study originates in areas of critical and subcritical slopes.  相似文献   

16.
The results from a～1 km resolution HYbrid Coordinate Ocean Model (HYCOM), forced by 1/2° Navy Operational Global Atmospheric Prediction System (NOGAPS) atmospheric data, were used in order to study the dynamic response of the Persian Gulf to wintertime shamal forcing. Shamal winds are strong northwesterly winds that occur in the Persian Gulf area behind southeast moving cold fronts. The period from 20 November to 5 December 2004 included a well defined shamal event that lasted 4–5 days. In addition to strong winds (16 m s?1) the winter shamal also brought cold dry air (Ta=20 °C, qa=10 g kg?1) which led to a net heat loss in excess of 1000 W m?2 by increasing the latent heat flux. This resulted in SST cooling of up to 10 °C most notably in the northern and shallower shelf regions. A sensitivity experiment with a constant specific humidity of qa=15 g kg?1 confirmed that about 38% of net heat loss was due to the air–sea humidity differences. The time integral of SST cooling closely followed the air–sea heat loss, indicating an approximate one-dimensional vertical heat balance. It was found that the shamal induced convective vertical mixing provided a direct mechanism for the erosion of stratification and deepening of the mixed layer by 30 m. The strong wind not only strengthened the circulation in the entire Persian Gulf but also established a northwestward flowing Iranian Coastal Current (ICC, 25–30 cm s?1) from the Strait of Hormuz to about 52°E, where it veered offshore. The strongest negative sea level of 25–40 cm was generated in the northernmost portion of the Gulf while the wind setup against the coast of the United Arab Emirates established a positive sea level of 15–30 cm. The transport through the Strait of Hormuz at 56.2°E indicated an enhanced outflow of 0.25 Sv (Sv≡106 m3 s?1) during 24 November followed by an equivalent inflow on the next day.  相似文献   

17.
The interaction between waves and artificial reefs (ARs; a hollow cube weighing 8.24 kN (0.84 t) and a water pipe weighing 1.27 kN (0.13 t)) in shallow waters was investigated with respect to variations in design weight, orientation (for cube; 45° and 90° angles, for pipe; 0°, 90°, and 180° angles to flow), depth (1–20 m), and bottom slope (10?1, 30?1, and 50?1). Physics equations and FLUENT software were used to estimate resisting and mobilising forces, and drag coefficients. Drag coefficients for the hollow cube were 0.76 and 0.85 at 45° and 90° angles to the current, respectively, and 0.97, 0.38, and 1.42 for the water pipe at 0°, 90°, and 180° angles to the current, respectively. Deepwater offshore wave conditions at six stations were transformed into shallow nearshore waters representative of the artificial reef site. Waters deeper than 12 and 16 m are safe to deploy blocks with angles of 45° and 90°, respectively. However, water pipes constructed at angles of 90° and 180° to the current were estimated as being unstable for 365 out of 720 cases at all stations (only one station was stable for all cases). Water pipes angled at 0° were found to be stable in all 360 cases. Slope had a significant effect on weight and depth. Results from this study provide an important reference for engineers performing projects aiming to increase the performance and service life of ARs.  相似文献   

18.
This study was performed in order to obtain information on the influence of an acute anoxic event (September, 1997) on distribution and speciation of inorganic iodine in the water column of a small, intensely eutrophicated salt lake. The variations in iodate and iodide depth distributions during the investigated period (1998–2000) were in accord with seasonal changes in redox conditions. During the stratification period (spring and summer), the concentration ratio between iodate and iodide in the upper layers was high, whereas during late summer and autumn, as a result of water column de-stratification and mixing of highly reducing deep water with the oxic layer, lower ratios and more uniform depth distributions were observed.The massive mortality of lake organisms induced by anoxic conditions and sulphide presence throughout the water column was registered by the end of September 1997, when overturn of the lake occurred. The concentrations of iodate in the oxic upper layers were elevated for more than a year after the mass-mortality event (up to 0.55 μmol L−1), whereas iodide concentrations remained high for more than 2 years in deep anoxic water (up to 2.27 μmol L−1). These data suggest that biogeochemical renewal processes affecting the concentrations of inorganic iodine in the lake water are slow compared to those that govern the speciation of iodine. The role of sediment–water interactions and iodine-rich organic species in the production of iodide are discussed.  相似文献   

19.
The Amazon River Plume delivers freshwater and nutrients to an otherwise oligotrophic western tropical North Atlantic (WTNA) Ocean. Plume waters create conditions favorable for carbon and nitrogen fixation, and blooms of diatoms and their diazotrophic cyanobacterial symbionts have been credited with significant CO2 uptake from the atmosphere. The fate of the carbon, however, has been measured previously by just a few moored or drifting sediment traps, allowing only speculation about the full extent of the plume's impact on carbon flux to the deep sea. Here, we used surface (0.5 m) sediment cores collected throughout the Demerara Slope and Abyssal Plain, at depths ranging from 1800 to 5000 m, to document benthic diagenetic processes indicative of carbon flux. Pore waters were extracted from sediments using both mm- and cm-scale extraction techniques. Profiles of nitrate (NO3) and silicate (Si(OH)4) were modeled with a diffusion-reaction equation to determine particulate organic carbon (POC) degradation and biogenic silica (bSi) remineralization rates. Model output was used to determine the spatial patterns of POC and bSi arrival at the sea floor. Our estimates of POC and Si remineralization fluxes ranged from 0.16 to 1.92 and 0.14 to 1.35 mmol m−2 d−1, respectively. A distinct axis of POC and bSi deposition on the deep sea floor aligned with the NW axis of the plume during peak springtime flood. POC flux showed a gradient along this axis with highest fluxes closest to the river mouth. bSi had a more diffuse zone of deposition and remineralization. The impact of the Amazon plume on benthic fluxes can be detected northward to 10°N and eastward to 47°W, indicating a footprint of nearly 1 million km2. We estimate that 0.15 Tmol C y−1 is remineralized in abyssal sediments underlying waters influenced by the Amazon River. This constitutes a relatively high fraction (~7%) of the estimated C export from the region.; the plume thus has a demonstrable impact on Corg export in the western Atlantic. Benthic fluxes under the plume were comparable to and in some cases greater than those observed in the eastern equatorial Atlantic, the southeastern Atlantic, and the Southern Ocean.  相似文献   

20.
Data collected from hydrographic stations occupied within the Venezuelan and Columbian basins of the Caribbean Sea from 1922 through 2003 are analyzed to study the decadal variability of deep temperature in the region. The analysis focuses on waters below the 1815-m sill depth of the Anegada–Jungfern Passage. Relatively dense waters (compared to those in the deep Caribbean) from the North Atlantic spill over this sill to ventilate the deep Caribbean Sea. Deep warming at a rate of over 0.01 °C decade–1 below this sill depth appears to have commenced in the 1970s after a period of relatively constant deep Caribbean Sea temperatures extending at least as far back as the 1920s. Conductivity–temperature–depth station data from World Ocean Circulation Experiment Section A22 along 66°W taken in 1997 and again in 2003 provide an especially precise, albeit geographically limited, estimate of this warming over that 6-year period. They also suggest a small (0.001 PSS-78, about the size of expected measurement biases) deep freshening. The warming is about 10 times larger than the size of geothermal heating in the region, and is of the same magnitude as the average global upper-ocean heat uptake over a recent 50-year period. Together with the freshening, the warming contributes about 0.012 m decade–1 of sea level rise in portions of the Caribbean Sea with bottom depths around 5000 m.  相似文献   

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