High Suspended Particulate Matter Concentrations Research Articles

Diurnal Characteristics of Suspended Particulate Matter and PM2.5 in the Urban and Suburban Atmosphere of the Kanto Plain, Japan

Suspended particulate matter (SPM) and PM2.5 in the urban and suburban atmosphere of the Kanto Plain of Japan, which includes the Tokyo metropolitan area, during the period 22–26 July 2002 were characterized. Samples of SPM and PM2.5 were collected by low-volume samplers at 6-h intervals at Suginami, Saitama, and Kisai. At all the sites, the major components of SPM and PM2.5 were organic carbon (OC), elemental carbon (EC), and sulfate. The ion balance, the size distributions of the ionic species, and the high correlation between SO4 2− and NH4 + indicated that the main chemical form of sulfate was (NH4)2SO4. The OC/EC ratios were larger in the daytime than in the nighttime. The correlation coefficients of OC, OC/EC, and SO4 2− with ozone concentrations at inland sites (Saitama, Kisai) were higher than those at the coastal site (Suginami). Bound water and hydrogen and oxygen atoms associated with OC, the amounts of which were estimated with a mass closure model, contributed substantially to the total particle mass. The chemical characteristics of the particles indicated that two mechanisms led to high concentrations of SPM and PM2.5: (i) an active photochemical process produced high concentrations of OC and sulfate, leading to a high concentration of (NH4)2SO4 in the particles and to production of secondary organic aerosols; (ii) stable meteorological conditions resulted in accumulation of primary particles, mainly emitted from vehicle exhaust, resulting in high concentrations of OC and EC.

Spatial distribution and trophic ecology of dominant copepods associated with turbidity maximum along the salinity gradient in a highly embayed estuarine system in Ariake Sea, Japan

The present study aimed to investigate into the feeding ecology of the dominant copepods along a salinity gradient in Chikugo estuary. Copepod composition was studied from samples collected from stations positioned along the salinity gradient of the estuary. Copepod gut pigment concentrations were measured by fluorescence technique and hydrographical parameters such as temperature, salinity, transparency, suspended particulate matter (SPM); pigments such as chlorophyll- a (Chl- a), phaeopigment; and particulate nutrients such as particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured. Two distinct zones in terms of nutrient and pigment concentrations as well as copepod distribution and feeding were identified along the estuary. We identified a zone of turbidity maximum (TM) in the low saline upper estuary which was characterized by having higher SPM, higher POC and PON but lower POC:PON ratios, higher pigment concentrations but lower Chl- a/SPM ratios and higher copepod dry biomass. Sinocalanus sinensis was the single dominant copepod in low saline upper estuary where significantly higher concentrations of nutrients and pigments were recorded and a multispecies copepod assemblage dominated by common coastal copepods such as Acartia omorii, Oithona davisae and Paracalanus parvus was observed in the lower estuary where nutrient and pigment concentrations were lower. Copepods in the estuary are predominantly herbivorous, feeding primarily on pigment bearing plants. However, completely contrasting trophic environments were found in the upper and the lower estuary. It was speculated from the Chl- a and phaeopigment values that copepods in the upper estuary receive energy from a detritus-based food web while in the lower estuary an algal-based food web supports copepod growth. Overall, the upper estuary was identified to provide a better trophic environment for copepod and is associated with higher SPM concentrations and elevated turbidity. The study demonstrates the role of estuarine turbidity maximum (ETM) in habitat trophic richness for copepod feeding. The study points out the role of detritus-based food web as energy source for the endemic copepod S. sinensis in the upper estuary, which supports as nursery for many fish species.

Mudflats and mud suspension observed from satellite data in French Guiana

The littoral of French Guiana is characterized by the north-westward migration of large mud banks along shore and by high suspended particulate matter concentrations (SPMC) coming from the Amazon River. A correspondence function is established between in situ optical data and SPMC measurements obtained from three coastal surveys on the Kaw River, the Mahury estuary, and the adjacent continental shelf, respectively. This function is applied to SPOT satellite images to estimate SPMC distributions near the sea surface on five dates between 1998 and 2001. Two typical situations have been observed: the mud suspensions are generally confined near the coast by a strong north-westward coastal current, while in one case (SPOT scene of 2 July 2001) the turbid plumes, probably resulted from the wave action on the mud banks, are directed seaward. SPMC varies from more than 300 mg l −1 adjacent to the intertidal zone to a few mg l −1 offshore. Turbid plumes are observed downstream, with regard to the Guyana Current, of small islands along the coast. Mud undulations are observed on the emergent surface of the mudflats, parallel to the crest waves and characterized by a wavelength of 200–1000 m. These structures are interpreted to form by wave action on the soft mudflat surface. Mangrove colonization of the mudflat follows these primary topographic structures.

Diffuse attenuation coefficients Kd(PAR) at the estuarine North Sea–Baltic Sea transition: time-series, partitioning, absorption, and scattering

The study is based on a 1 year record ( n=46) of the diffuse attenuation coefficient— K d(PAR) (m −1)—in combination with CTD-casts at one position in Århus Bay, Kattegat, the North Sea–Baltic Sea estuarine transition. Water samples were collected occasionally for determination of suspended particulate matter (SPM) and chromomorphic dissolved organic matter (CDOM). The K d(PAR) varied between 0.152 and 0.557 (m −1) with an average of 0.293 (m −1). The depth of the photic zone (1% light level) varied between 8.3 and 15.7 m at maximum and average K d(PAR). Maximum K d(PAR) values occurred in periods of high chl-a concentrations. The average CDOM absorption coefficient was 0.232 (m −1) whereas the average chl-a and inorganic SPM concentrations equalled 3.3 (mg m −3) and 4.5 (g m −3). Light attenuation partitioning in percent was: water (9), CDOM (17), SPM (42), and phytoplankton (32) at average conditions. Attenuation by phytoplankton reached up to 74% at high chl-a concentrations whereas SPM light attenuation reached 45% at high SPM concentrations. Results show that light attenuation in the bay is governed by phytoplankton and SPM concentrations whereas CDOM is of less significance. Light absorption in the PAR range— a(PAR)—ranged between 0.262 (m −1) at average conditions and 0.49 (m −1) at maximum phytoplankton concentrations. Scattering was governed by SPM at average conditions whereas phytoplankton scattering was higher than SPM scattering at chl-a concentrations >4.5 (mg m −3).

SPM transport in the Bohai Sea: field experiments and numerical modelling

The suspended particulate matter (SPM) concentration in the Bohai Sea, China, is measured during two cruises carried out from September to October 1998 and April to May 1999. The analysis of the in-situ data reveals two zones of high SPM concentration that can be attributed to Yellow River water as well as to resuspension. The exchange with water masses of the Yellow Sea leads to a reduction of the SPM concentration in the eastern and central part of the Bohai Sea. The field data also show that in the Bohai Sea the wind waves strongly influence the SPM concentrations. This explains the major part of the seasonal variation: the SPM concentration is higher in spring than in summer, which results from the seasonal variation of the wind. A 3D numerical SPM transport model is used in this study to simulate the conditions during two cruises that have been conducted in the frame of the project. The results show that the model can well reproduce the observed SPM concentrations in the Bohai Sea. The results also agree well with SeaWiFS satellite data taken during one of the cruises.

Trace metal behaviour in the Conwy estuary, North Wales

The distribution of trace metals Zn, Ni, Mn, Fe, Cu, Pb, Cd and Cr between suspended particulate matter (SPM) and water in the Conwy estuary, North Wales, has been studied in three surveys in 1998. Dissolved Cu and Mn showed some monthly variations. Most of the dissolved trace metals displayed a negative association with salinity, indicating rivers as a major source of inputs for them. Particulate Zn, Mn and Fe showed a decreasing concentration seaward, whilst the levels of Ni, Cu, Cr and Pb increased with salinity. SPM concentration was the most important variable significantly related to trace metal concentrations in SPM, with an inverse relationship between the two parameters. This was explained by the relative enrichment of trace metals in fine particles at low SPM concentrations and relative depletion of trace metals in coarse particles at high SPM concentrations. Particulate Zn, Mn and Pb were dominated by the fraction available to acetic acid (non-detrital), whilst particulate Ni, Fe and Cr were dominated by the fraction available to nitric acid (detrital). The partition coefficient of trace metals between SPM and water declined with increasing SPM concentration, consistent with the so-called “particle concentration effect”. Such a phenomenon may be explained by the presence of fine particles (including colloids) enriched with trace metals at low SPM concentrations, and the salinity-induced desorption.

The dependence of estuarine turbidity on tidal intrusion length, tidal range and residence time

It is shown that there is a marked tendency for long, strongly tidal estuaries to have greater suspended particulate matter (SPM) concentrations within their high-turbidity regions than shorter estuaries with comparable tidal ranges at their mouths, or weakly tidal estuaries. Using consistently derived data from 44 estuaries in Europe and the Americas, contours of the logarithm of maximum estuarine SPM concentration are shown to be reasonably smooth when plotted against the logarithm of mean spring tidal range (at the estuary mouth) and the logarithm of estuarine tidal length. Predictions from the plot are compared with published observations made in the Delaware, Scheldt, Rio de la Plata, Gironde, Bay of Fundy, Changjiang (Yangtze), Amazon, Patos Lagoon and the Hawkesbury Estuary and it is shown that, qualitatively, there are no serious discrepancies. Short, weakly tidal estuaries are predicted to have very low ‘intrinsic’ SPM concentrations. High SPM concentrations in these estuaries would most likely be the result of either locally generated wave resuspension, high freshwater sediment loads due to freshets, or intruding seawater carrying suspended sediments derived from wave activity in the coastal zone. Application of a generic tidal model demonstrates that longer estuaries possess faster tidal currents for a given tidal range at their mouth and, in the presence of a supply of erodable fine sediment, therefore (by implication) produce greater concentrations of SPM that can be accumulated within a turbidity maximum. The same is true if the tidal range is increased for estuaries of a given length. These features are illustrated by comparing surveys of SPM data from two large estuaries possessing greatly different tidal ranges (the microtidal, medium turbidity Potomac and the macrotidal, highly turbid Humber-Ouse) and a third, much smaller but strongly tidal estuary (the low-turbidity Tweed). It is demonstrated that longer estuaries tend to have longer flushing times for solutes than shorter systems and that larger tides tend to reduce flushing times, although the tidal influence is secondary. Short, rapidly flushed estuaries quickly lose their erodable fine sediment to the coastal zone during freshets and during the ebbing currents of spring tides. Turbidity is therefore small during low runoff, low wave activity conditions. Very long, very slowly flushed estuaries are unlikely to lose a significant fraction of their resuspended sediments during freshets or individual ebb tides and are therefore able to accumulate large and increasing amounts of fine sediment in the long-term. Turbidity within them is therefore high during the fast currents of large spring tides.

Effect of winds on SO 2 and SPM concentrations in Delhi

A study of concentrations of sulfur dioxide (SO 2) and suspended particulate matter (SPM) has been performed in Delhi. The monthly and seasonal variations of concentrations and winds are analyzed. The monthly mean SO 2 concentrations were in the range of 16.15–34.44 μg m −3 and showed regular seasonal variations with the highest concentrations in winter and lowest in monsoon season. On the other hand, the monthly mean SPM concentrations reached the highest (465.68 μg m −3) in November and the lowest (150.07 μg m −3) in August. It was observed that high SO 2 concentrations were generally associated with the wind blowing from WNW–NW directions, and the high SPM concentrations were usually related to the wind blowing from W–NW directions.

Spectral remote sensing reflectances of coastal waters in French Guiana under the Amazon influence

The French Guiana coast, located about 500 km north of the Amazon mouth, is characterized by mangroves and large mud banks migrating northwestwards. These banks are composed of fine clay sediments originating from the Amazon River. In November 1998, field work was carried out on the Mahury River to measure the water colour and the concentration of suspended particles in surface water. An increase of the remote sensing reflectance due to high concentration of mineral particles was observed. The Mahury River survey (November 1998), together with an oceanographic survey onboard the ANTEA vessel (PRECHICO cruise, April 1999), enabled us to identify several classes of remote sensing reflectance spectra characterizing the continental shelf between Cayenne and the Brazil frontier: (1) light blue waters above the shelf break; (2) low salinity dark brown waters above the continental shelf, originating from the Amazon River; (3) green waters above the 20-m isobath; and (4) beige waters close to the coast and in the rivers mouths. The normalized water leaving radiances (nLw) computed from these spectra in the spectral bands of SeaWiFS are examined. The standard OC2 performs poorly in retrieving chlorophyll from the reflectance data because of the relatively high suspended particulate matter concentrations.

Suspended particulate matter fluxes through the Straits of Dover, English Channel: observations and modelling

Suspended Particulate Matter (SPM) concentrations at various levels within the water column, together with salinity and temperature, were measured using water samples collected from six stations across the Straits of Dover. The sampling programme covered a 16-month period, undertaken during 23 cruises. On the basis of the spatial variability in the concentrations, the water bodies are divided by several boundaries, controlled by tidal and wind conditions. Within the water column, SPM concentrations were higher near the sea bed than in the surface waters. Throughout the cross-section, maximum concentrations occurred adjacent to the coastlines. Temporal variability in the SPM concentration exists on daily and seasonal scales within the coastal waters (4.2 to 74.5 mg·L −1): resuspension processes, in response to semi-diurnal tidal cycles (with a period of around 12.4 h) and spring-neap cycles (with a period of 15 days) make significant contributions. Distinctive seasonal/annual concentration changes have also been observed. In the offshore waters, such variability is much less significant (0.9 to 6.0 mg·L −1). In the summer the English Coastal Zone is associated with relatively high SPM concentrations: the Central Zone has a low and stable SPM concentration between these zones, there is a Transitional Zone, where there is a rapid response of SPM concentration to wind forcing. Finally, the French Coastal Zone is characterized by variable (sometimes high) SPM concentrations. Because of the zonation, SPM fluxes within the Dover Strait are controlled by different transport mechanisms. Within the Central Zone, the flux can be represented by the product of mean water discharges and SPM concentrations. However, within the coastal zones fluctuations in SPM concentrations on various time-scales must be considered. In order to calculate the maximum and minimum SPM fluxes, 10 cells were divided in the strait. A simple modelling calculation has been proposed for this complex area. The effect of spring-neap tidal cycles and seasonal changes can contribute significantly to the overall flux, which is of the order of 20×10 6 t·yr −1 (through the Dover Strait, towards the North Sea). Such an estimate is higher than most obtained previously. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS suspended particulate matter / flux / transport mechanisms / straits / English Channel

Distribution of suspended particulate matter determined by in-situ observations and satellite images in the NW Aegean Sea (Greece)

Suspended particulate matter (SPM) patterns in the surface waters of the NW Aegean Sea were studied by (1) determining SPM concentration by water filtration, (2) measuring light transmission, and (3) evaluating satellite images. The SPM signals of the three major rivers discharging into the study area were recorded by all three methods, thereby providing information about the sources, transport pathways, and regional dispersion patterns of the SPM. The filtration of water samples and light transmission measurements were found to be good indicators of SPM concentrations in surface waters. Most of the SPM is composed of terrigenous minerals, thus explaining the correlation between the beam attenuation coefficient and the SPM concentration. A Landsat image obtained for the study period was found to adequately reveal regions with high SPM concentrations. Low concentrations, on the other hand, remain obscured.

Impact of suspended particulate matter on egg production of the estuarine copepod, Eurytemora affinis

Egg production rate and gut pigment content of Eurytemora affinis were measured in the Gironde, Westerschelde and Elbe estuaries. These represent various conditions with respect to suspended particulate matter (SPM) concentration. Egg production rate varied as a function of temperature and was strongly affected by high SPM concentration. Specific gut pigment content (Gsp) and specific pigment ingestion also clearly decreased when SPM concentration increased, suggesting that SPM concentration could influence egg production rate through a vegetal prey uptake limitation and that E. affinis either gained an energetic advantage by vegetal prey ingestion or needed vegetal prey in order to obtain a minimum amount of specific component required for egg production.

Grazing activity of mesoplanktonic copepods in a shallow bay during an algal spring bloom (Marennes-Oléron Bay, France)

In situ grazing activity of mesoplanktonic copepods was investigated by the fluorometric method during an algal spring bloom in a zone of oyster farming in Marennes-Oléron Bay. The grazing activity of copepods was overall higher during the night than during the day for three species (Temora longicornis, Paracalanus parvus and Acartia clausi), but peaks also appeared during the day for all of them. Individual ingestion rates and daily rations were higher during neap tide (low suspended particulate matter (SPM) concentrations) than during spring tide (high SPM concentrations). During ebb tide (when SPM concentrations were the lowest) the feeding activity of T. longicornis, P. parvus and A. clausi was significantly negatively correlated with algal concentration. Our work suggests that during the algal spring bloom in the farming area of Marennes-Oléron Bay the pressure exerted by mesoplanktonic copepods on the algal stock was very low, as a consequence of: (i) high algal concentrations in the field (resuspension and high phytoplanktonic production); (ii) low ingestion rates when high algal concentrations were observed. The likely ingestion of non-fluorescent particles by copepods is discussed.

Stoichiometry of carbon, hydrogen, nitrogen, sulfur and oxygen in the particulate matter of the western North Pacific marginal seas

Abstract The suspended particulate matter (SPM) in surface seawater was collected from 19 stations in the Sea of Japan, 42 stations in the East China Sea, 7 stations North of Taiwan and 6 stations in the Philippine Sea and the Bashi Channel. The particulate organic carbon (POC), particulate organic hydrogen (POH), particulate organic nitrogen (PON), particulate organic sulfur (POS), particulate organic oxygen (POO), particulate phosphorus (PP) and total organic matter (TOM) concentrations were determined. In the Sea of Japan these concentrations were generally lower in the region affected by the Kuroshio branch. In the East China Sea high concentrations of SPM and other organic components were found at stations nearest the Yangtze River mouth, reflecting the terrestrial input. On the other hand, the values were lower in regions influenced by the Kuroshio. In the Philippine Sea and the Bashi Channel, the effect of terrestrial input was not obvious, resulting in lower concentrations of organic matter. The average molar ratios for all samples were C:H:N:S:O = 7.69(± 0.33): 8.73(± 1.62): 1.0: 0.16(± 0.014): 4.12(± 0.64).

Patterns and controls of the suspended matter distribution over the shelf and upper slope south of New England

A well defined pattern of suspended particulate matter (SPM) distribution is seen in transmissometer transects taken on the shelf and upper slope south of New England during eight SEEP-I cruises carried out in different seasons of the year. Higher concentrations of SPM are located in the shallow part of the shelf (<60m), and along the foot of the shelf-slope front. Between these two areas SPM concentrations decrease to relatively low values. Seaward from the foot of the front, SPM concentrations decrease, but a significant increase is clearly detected near the shelf break where an intrusion of slope water, seen as a salinity maximum, intersects with the seabed. This distribution pattern is quite persistent throughout the year, although SPM concentrations change according to hydrodynamic and biological conditions. Persistent maxima in near-bottom SPM concentration, associated with the foot of the shelf-slope front and with the slope water intrusion, had not been observed before, either in this or in any other area. The SPM distribution in the study area is controlled by several different processes. An SPM maximum of primarily biological material is associated with the spring-summer thermocline, but not at other seasons. Surface waves generate persistent high SPM concentrations over the shelf shallower than 60 m. The high SPM values along the foot of the front and along the intersection of the slope water intrusion with the seabed are produced by the interaction of processes such as internal waves, and tides with these hydrographic frontal gradients. Sediment resuspended by these mechanisms is transported along the isobaths of the shallow shelf, along the foot of the shelf-slope front, and along the intersection of the slope water intrusion with the seabed, following the advective, mean flow. This distribution of near-bottom SPM is not related to the nature of the underlying sediment, but is controlled by the interaction of hydrographic and dynamic processes.

A note on the factors controlling the sedimentation rate along the western continental shelf of India

To study variations in sediment accumulation along the western continental shelf of India, sedimentation rates have been measured in two cores from the shelf off Mangalore. The rates obtained are 0.72 and 0.56 mm/yr for water depths of 35 and 45 m respectively. These are significantly lower than those of the northern continental shelf (north of 18°N) where sedimentation rates range between 1.8 and 19 mm/yr. The low rates in the southern area are due to the low concentrations of suspended particulate matter (SPM) coming from rivers such as the Netravati and Gurpur that drain into the study area. These rivers contribute only about 8% of the total discharge of all the west-flowing rivers of the Indian peninsula, whereas rivers flowing onto the northern continental shelf have high SPM concentrations and contribute about 45% of the total discharge of the west-flowing rivers. The occurrence of outer shelf sands ranging in age from 9000 to 11,000 yrs B.P. at various depths below mean sea level in the northern and southern parts of the western continental shelf may be indicative of neotectonic activity, and the presence of such activity is supported by the occurrence of recent earthquakes and hot springs in Western India, the northward compression of the Western Indian continental margin, coastal geomorphic features and epeirogenic movement of the West Indian landmass. However, it could also be the result of differing influxes of terrigenous sediment and of riverine particulates travelling over different distances into the Arabian Sea.

Seasonality and composition of particulate fluxes during ECOMARGE—I, western Gulf of Lions

As part of the ECOMARGE program (ECOsystèmes de MARGE continentale), sequential sediment traps were deployed on the continental margin of the Gulf of Lions, in the northwestern Mediterranean Sea. Two sites located in the southwestern part of this region were selected for the first phase of the experiment: inner shelf (bottom depth: 27 m) and continental slope (Lacaze-Duthiers Canyon, bottom depth: 650 m). The canyon was selected as representative of the continental slope, because canyons comprise more than 50% of the slope area. Total mass, organic matter, opal, carbonate and siliciclastic residue fluxes were measured biweekly at 50, 100, 300 and 600 m in the upper part of the Lacaze-Duthiers Canyon (from July 1985 to April 1986) and for longer periods (2 weeks to 2 months) at 10 and 25 m on the shelf (from May 1985 to June 1986). Mass fluxes increased generally with depth, reaching values as high as 20,000 mg m −2 d −1 in the 600 m slope (canyon) trap; this indicated lateral transport of biogenic and abiogenic particulate matter, from local (adjacent shelf and upper slope waters) and distant origin (Rhoˆne River). Shelf-slope particulate transfer attested by the paracontemporaneity of high flux events on the shelf and the slope and by the continuity of the shelf benthic nepheloid layer and intermediate nepheloid layers over the canyon: this rapid and took generally less than 16 days (trap sample resolution time). Particle fluxes and compositions defined a layered system, in which the surface layers< 100m) were essentially characterized by biogenic material (organic matter and opal), and deep layers chiefly characterized by the collection of elastic material (carbonate and siliciclastic material). Significant temporal increases in total mass and constituent fluxes showed two frequencies: a low seasonal frequency, which was related to seasonal variations of the Liguro-Provençal Current and to the winter increase of the Rhoˆne River and other coastal river discharges; variations at higher frequencies, which were related to various impulse events such as summer internal waves, autumn and winter storms and spring nutrient enrichment. The role of the Lacaze-Duthiers Canyon in the particulate transfer across the continental margin is discussed within the particular context of this advective system. Although the importance of local, intra-canyon resuspension of bottom sediments could not be estimated, it seems that the high suspended particulate matter concentrations and particle fluxes observed are essentially related to the fact that this canyon acts as a natural trap which collects particles from the entire Gulf of Lions. Comparison of the flux necessary to sustain the unsupported 210Pb inventory in the canyon sediments, with the mean 210Pb flux measured by traps and of 210Pb-determined mass accumulation rates with total mass fluxes indicate that the canyon partly acts as a modern sediment depocenter of the particles swept into it from the shelf and the slope; also partly as a modern conduit of particles to the deep basin. Several biological mechanisms are probably responsible for the rapid settling of particles onto the slope (within the canyon); these may, thereby, reduce lateral transfer from the shelf to the open ocean and constitute a kind of “biological barrier”.

The character and motion of suspended particulate matter over the shelf edge and upper slope off Cape Cod

Time series of suspended particulate matter (SPM) concentration made by transmissometers deployed on the shelf edge and upper slope off New England are examined together with data from companion sensors. At the shelf-edge instrument cluster (on the 125-m isobath) the highest SPM concentrations were apparently due to sediment resuspended further onshore and advected to the transmissometer by offshore motion of the shelf-edge density front. This was due to a tendency for more frequent episodes of high bottom stress, and thus more sediment resuspention, progressing onshore from the outer shelf. The decrease of surface wave current amplitude with depth was primarily responsible for this cross-shelf gradient in bottom stress. On one occasion very turbid water was observed at the shelf edge when the bottom stress was low and the frontal motion was small. Data obtained from the U.S. National Marine Fisheries Service showed unusually intensive bottom trawling activity in the vicinity of the transmissometer during this event. This data further indicates that resuspension by trawlers may be an important source of suspended material on the shelf edge. The record of the transmissometer deployed over the upper slope indicates that transport of particulate material in suspension from the near bottom on the shelf into the slope region occurred primarily along density surfaces, and was not continuous but intermittent.

Circulation and sedimentation of suspended particulate matter in New Zealand fjords

Circulation in the New Zealand fjords is estuarine, with a seaward-flowing brackish layer overflowing saline water. Despite an extremely high rainfall (>6000 mm yr -1), terrestrial dediment input is low and concentrations of suspended particulate matter (SPM) rarely exceed 1 mg 1 -1. The terrestrial influence is barely detectable anywhere in the fjords; SPM in near-surface waters is dominated by phytoplankton. In surface waters, SPM components remain separate, as they settle they are clustered into larger groups by agglomeration, faecal pelletization and flocculation. Phytoplankton produce a secondary SPM maximum at the top of the deep zone. Deep waters are barren of living plankton with clustered SPM and broken phytoplankton settling from above. The low terrestrial SPM input and high organic/biogenic concentrations are reflected in low sedimentation rates and high organic carbon content of bottom sediments. The estuarine stratification is broken up in the fjord entrances by ocean waves which also resuspend sediment off the entrance sills thereby increasing SPM concentrations in bottom waters. High SPM concentrations are found in basins cut off from the main fjord by shallow sills which inhibit deep-water renewal.

Spatial distributions and variability of suspended particulate matter in warm-core ring 82B

Spatial distributions and variability of suspended particulate matter (SPM) were determined optically during CTD/transmissometer surveys of warm-core ring (WCR) 82B and surrounding waters in June 1982. SPM distributions within 30 km of ring center from the surface to the depth of the 27.6 kg m −3 potential density surface at 800 m were different from surrounding waters. Waters within this core region of the ring had higher SPM concentrations between potential densities of 26.0 and 26.75 kg m −3 and had lower concentrations between 26.8 and 27.5 kg m −3 when compared to sorrounding waters. This result suggests that processes within WCR 82B (as opposed to lateral exchange processes with surrounding waters) were most important in governing particle distributions near ring center. Such isolation was not true for entrainment zone waters 70–80 km from ring center. In this region, waters shallower than 100 m showed a strong influence of waters from the continental shelf. In the entrainment zone, SPM concentrations between the 26.8 and 27.5 kg m −3 potential density surfaces (between 100 and 380 m) were higher compared with waters of similar density both within the ring and in the surrounding Slope Water. In addition, higher SPM concentrations were found in the region of offshore flow behind the ring than in the onshore flow ahead of the ring. This produces a net offshore transport of SPM by WCR 82B for entrainment zone waters of this potential density interval of between 2900 and 15,800 g SPM s −1. These results suggest that WCR's may be very important in the dispersal of resuspended continental slope sediments 100–200 km away from the continental margin.