A benthic storm in the northeastern tropical Pacific over the fields of manganese nodules

doi:10.1016/0967-0637(94)90019-1

Deep Sea Research Part I: Oceanographic Research Papers

Volume 41, Issue 7, July 1994, Pages 1069-1089

https://doi.org/10.1016/0967-0637(94)90019-1 Get rights and content

Abstract

Studies in the northeastern tropical Pacific over 5 years have revealed high eddy activity in the region. Measurements show considerable space-time variation in the bottom currents. A near-bottom intensification in the current velocity over the bottom boundary layer (BBL) has been recorded. A benthic storm (BS) lasting about 10 days, at a maximum measured velocity of 13 cm s⁻¹ 6 m above the bottom, appeared to be related to eddies extending to the bottom. The action of these eddies can lead to a change in the direction of the bottom currents and an increase in their velocity. This action also manifests itself by a change in the depth of the benthic thermocline, a reduction in its thickness and in the temperature gradient, as well as in a transformation of the Antarctic Bottom Water (AABW) and the emergence of bottom fronts.

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Cited by (30)

Environment, ecology, and potential effectiveness of an area protected from deep-sea mining (Clarion Clipperton Zone, abyssal Pacific)
2021, Progress in Oceanography
Citation Excerpt :
Peak velocities of up to 0.25 m s−1 have been registered (Aleynik et al., 2017; Amos and Roels, 1977). Deep low-frequency currents intensify in the bottom boundary layer within ~ 100–30 m from the seabed in this region and veer counter-clockwise toward the bottom consistent with an Ekman layer dynamic (Hayes, 1980; Kontar and Sokov, 1994). In addition, higher-frequency internal inertia-gravity waves, including semidiurnal tides and near-inertial waves, are generated by barotropic tides, eddies and mean currents flowing over rough topography, which includes seamounts, ridges, and troughs present in the APEI-6 area.
To protect the range of habitats, species, and ecosystem functions in the Clarion Clipperton Zone (CCZ), a region of interest for deep-sea polymetallic nodule mining in the Pacific, nine Areas of Particular Environmental Interest (APEIs) have been designated by the International Seabed Authority (ISA). The APEIs are remote, rarely visited and poorly understood. Here we present and synthesise all available observations made at APEI-6, the most north eastern APEI in the network, and assess its representativity of mining contract areas in the eastern CCZ. The two studied regions of APEI-6 have a variable morphology, typical of the CCZ, with hills, plains and occasional seamounts. The seafloor is predominantly covered by fine-grained sediments, and includes small but abundant polymetallic nodules, as well as exposed bedrock. The oceanographic parameters investigated appear broadly similar across the region although some differences in deep-water mass separation were evident between APEI-6 and some contract areas. Sediment biogeochemistry is broadly similar across the area in the parameters investigated, except for oxygen penetration depth, which reached >2 m at the study sites within APEI-6, deeper than that found at UK1 and GSR contract areas. The ecology of study sites in APEI-6 differs from that reported from UK1 and TOML-D contract areas, with differences in community composition of microbes, macrofauna, xenophyophores and metazoan megafauna. Some species were shared between areas although connectivity appears limited. We show that, from the available information, APEI-6 is partially representative of the exploration areas to the south yet is distinctly different in several key characteristics. As a result, additional APEIs may be warranted and caution may need to be taken in relying on the APEI network alone for conservation, with other management activities required to help mitigate the impacts of mining in the CCZ.
Sedimentary condensation
2016, Earth-Science Reviews
Citation Excerpt :
At the site of Kane Gap (east Atlantic) the ferromanganese nodule carpets are considered as residual material concentrated during exceptional erosional events (Hartmann et al., 1989). Such erosional events are probably related to shortlasting “benthic storms”, which result from an eddie-related intensification in the bottom-current velocity (Kontar and Sokov, 1994). Fossil occurrences of ferromanganese nodules also indicate the importance of condensation processes in their formation and accumulation.
The term “condensation” has been used in sedimentological research for 180 years and ever since the last 80 years, its interpretation has become increasingly diverse and, to a certain degree, also divergent. The result is that today, the different definitions are not always compatible and therefore useful. It is for this reason that the term “condensation” is newly defined here, using the original descriptions from before 1930 and a new interpretation of condensed sediments, which were the subject of the first monograph dedicated to condensation (Heim and Seitz, 1934).
Condensed sediments are present in mostly well individualized, extremely thin (< 1 m) beds, which were formed during extremely long time periods (> 100 ky), and which experienced authigenesis and the precipitation of glaucony, verdine, phosphate, iron and manganese oxyhydroxides, iron sulfide, carbonate and/or silica. They usually show complex internal stratigraphies, which result from an interplay of sediment accumulation, halts in sedimentation, sediment winnowing, erosion, reworking and bypass. They may include amalgamated faunas of different origin and age. Hardgrounds may be part of condensed beds and may embody strongly condensed beds by themselves.
Sedimentary condensation is the result of a hydrodynamically active depositional regime, in which sediment accumulation, winnowing, erosion, reworking and bypass are processes, which alternate as a function of changes in the location and intensity of currents, and/or as the result of episodic high-energy events engendered by storms and gravity flow. The definition proposed here excludes the use of the term “condensed” in sequence-stratigraphic approaches, unless condensed beds as defined here are present. The term “condensed” in a sequence stratigraphic sense may be replaced by “sediment starved”.
Sedimentary condensation has been and still is a widespread phenomenon in past and present-day oceans. The present-day distribution of glaucony and verdine-rich sediments on shelves and upper slopes, phosphate-rich sediments and phosphorite on outer shelves and upper slopes, ferromanganese crusts on slopes, seamounts and submarine plateaus, and ferromanganese nodules on abyssal seafloors is a good indication of the importance of condensation processes today. In the past, we may add the occurrence of oolitic ironstone, carbonate hardgrounds, and eventually also silica layers in banded iron formations as indicators of the importance of condensation processes. Besides their economic value, condensed sediments are useful both as a carrier of geochemical proxies of paleoceanographic and paleoenvironmental change, as well as the product of episodes of paleoceanographic and paleoenvironmental change themselves.
Changes in abundance and community structure of nematodes from the abyssal polymetallic nodule field, Tropical Northeast Pacific
2015, Deep-Sea Research Part I: Oceanographic Research Papers
Citation Excerpt :
Benthic storms (bottom currents with a velocity>13–15 cm/s which are induced by meteorological variability at the ocean water surface) and geological activity may also influence deep-sea living communities. Benthic storms have been observed in the CCFZ (Kontar and Sokov, 1994; Demidova and Kontar, 1989; Le Suavé et al., 1990; Skornyakova and Murdmaa, 1992; Demidova, 1999; Hannides and Smith, 2003). These periodic events can cause erosion and redistribution of seafloor sediments and lead to spatial and temporal heterogeneity in food resources (Hollister and Heezen, 1972; Stow et al., 2009; Hernández-Molina et al., 2011).
Deep-sea fields of polymetallic nodules in the Clarion-Clipperton Zone (CCFZ, tropical NE Pacific) are currently being investigated to assess their potential for commercial mining. During such mining, benthic communities will be inevitably disturbed or destroyed. Therefore, assessments of their standing stock and composition may be helpful for the future evaluation of possible impacts of commercial nodule exploitation. Analysis of nematode communities (at genus level) inhabiting the French license area of the CCFZ were studied based on data from the cruises NODINAUT (2004) and BIONOD (2012). The total nematode density was ca. 1.5-fold higher in 2012 as compared with 2004. This reflected a 2–2.5 times higher density of non-selective deposit-feeders (i.e. possessing a small buccal cavity without armature) in 2012 compared with 2004, whereas no significant differences between sampling periods were observed in the density of the other feeding groups. Consequently, whilst the list of the most abundant genera was identical, their relative abundances changed significantly. The relative abundance of the genus Thalassomonhystera was two times greater in 2012 than in 2004, whereas the relative abundances of the genera Acantholaimus and Theristus were significantly lower in 2012 (10% and 4%, respectively) than in 2004 (28% and 9%). Nematode diversity (including values of diversity indices and total number of recorded genera) was significantly lower in 2012 in comparison with 2004. Although our data do not take into account seasonal and shorter temporal scales of variability in nematode assemblages, we report here that a certain fraction of variations observed between the two sampling periods could be associated with differences in primary production. Future studies should aim to better characterise temporal variability in nematode communities of the CCFZ at seasonal and interannual scales.
Submarine ridges do not prevent large-scale dispersal of abyssal fauna: A case study of Mesocletodes (Crustacea, Copepoda, Harpacticoida)
2011, Deep-Sea Research Part I: Oceanographic Research Papers
Citation Excerpt :
However, although many harpacticoids are relatively poor swimmers, passive transportation by means of bottom currents may enable considerable mobility (see Leese et al. (2010) and Pearse et al. (2008) for the remarkable mobility of benthic brooding crustaceans in the Southern Ocean). Bottom currents in the deep sea are generally slow, only few cm s−1, but regionally and occasionally several tens of cm s−1 (Gage and Tyler, 1991; Kontar and Sokov, 1994; Tyler, 2003 and references therein). Transport by currents may enable harpacticoids to find new sites or mates quickly.
We examined the large-scale distribution of deep-sea harpacticoid copepods at the species level, in order to clarify the underlying processes of copepod dispersal. The study was based on samples collected from 12 regions and a total of 113 stations: 57 stations at depths between 1107 and 5655 m on abyssal plains in the South and North Atlantic, Southern Ocean, southern Indian Ocean, and the Pacific Ocean, and 56 stations above 900 m in the North Atlantic and eastern Mediterranean Sea.
We chose the genus Mesocletodes Sars, 1909 as an ideal group to study the large-scale distribution of harpacticoid copepods in the deep oceans. Clear apomorphies and a comparatively large body size of about 1 mm allow rapid recognition of allied species in meiofauna samples. In addition, Mesocletodes represents more than 50% of the family Argestidae Por, 1986, one of the most abundant harpacticoid families in the deep sea.
The geographical distributions of 793 adult females of Mesocletodes belonging to 61 species throughout the South and North Atlantic, Southern Ocean, southern Indian Ocean, Pacific Ocean, and eastern Mediterranean Sea indicated that most species are cosmopolitan. Neither the topography of the sea bottom nor long distances seem to prevent species from dispersing. Passive transport by bottom currents after resuspension is likely the propulsive factor for the dispersal of Harpacticoida, while plate tectonics and movement of individuals in the sediment may play relatively minor roles.
Physical reworking by near-bottom flow alters the metazoan meiofauna of Fieberling Guyot (northeast Pacific)
1999, Deep-Sea Research Part I: Oceanographic Research Papers
Although much of the deep sea is physically tranquil, some regions experience near-bottom flows that rework the surficial sediment. During periods of physical reworking, animals in the reworked layer risk being suspended, which can have both positive and negative effects. Reworking can also change the sediment in ecologically important ways, so the fauna of reworked sites should differ from that of quiescent locations. We combined data from two reworked, bathyal sites on the summit of Fieberling Guyot (32°27.631′N, 127°49.489′W; 32°27.581′N, 127°47.839′W) and compared the results with those of more tranquil sites. We tested for differences in the following parameters, which seemed likely to be sensitive to the direct or indirect effects of reworking: (1) the vertical distribution of the meiofauna in the sea bed, (2) the relative abundance of surface-living harpacticoids, (3) the proportion of the fauna consisting of interstitial harpacticoids, (4) the ratio of harpacticoids to nematodes. We found that the vertical distributions of harpacticoid copepods, ostracods, and kinorhynchs were deeper on Fieberling. In addition, the relative abundance of surface-living harpacticoids was less, the proportion of interstitial harpacticoids was greater, and the ratio of harpacticoids to nematodes was greater on Fieberling. These differences between Fieberling and the comparison sites suggest that physical reworking affects deep-sea meiofauna and indicate the nature of some of the effects.
Growth of diagenetic ferromanganese nodules in an oxic deep-sea sedimentary environment, northeast equatorial Pacific
1999, Marine Geology
To study the accretion mechanism of diagenetic ferromanganese nodules formed in an oxic deep-sea sedimentary environment, manganese nodules, sediments, and pore waters were sampled in the northeast equatorial Pacific. Diagenetic ferromanganese nodules are ellipsoidal to discoidal in shape, rough in surface texture, enriched in Cu, Ni and 10 Å-manganite, and are ubiquitous on the abyssal plain; hydrogenetic nodules are polynucleated, irregular in shape, smooth in surface texture, enriched in Co and δ-MnO₂, and occur dominantly on seamounts. Numerous microlayers with diagenetic or hydrogenetic characteristics occur successively in the nodules. Concentration of nitrate in sediment pore waters indicates that overall redox conditions are oxic. However, Mn-oxide grains on the walls of burrows and worm tubes are interpreted to be reprecipitated metal ions supplied from oxygen-depleted microenvironments that formed in the oxic sediment column by decomposition of organic matter. Active mixing of bottom sediments by benthic fauna and bottom currents is indicated by ubiquitous burrows, worm tubes, and tracks and trails, high values in sediment mixing coefficients (>1 cm²/yr), and scattering of data points in depth profiles of pore water nitrate concentrations. We suggest that diagenetic ferromanganese nodules in an oxic deep-sea sedimentary environment grew from remobilized metal ions as well as reprecipitated Mn-oxide grains, which were supplied to the nodules episodically during the stirring of bottom sediments by benthic fauna and intermittent strong bottom current flow.

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A benthic storm in the northeastern tropical Pacific over the fields of manganese nodules

Abstract

Earth and Planetary Science Letters

Marine Geology

Deep-Sea Research

Netherland Journal of Sea Research

Marine Geology

Environmental aspects of nodule mining

Environmental baseline conditions in manganese nodule province

Flow structures of the benthic ocean

Journal of Geophysical Research

Topography of the North Pacific

Scripps Institute of Oceanography, IMP Tech. Rep. Series, TR-17