The benthic boundary layer (BBL) is the layer of water directly above the

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...

at the bottom of a

body of water A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such as p ...

(river, lake, or sea, etc.). It is generated by the

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...

of the water moving over the surface of the substrate. The thickness of this zone is determined by many factors, including the

Coriolis force In physics, the Coriolis force is an inertial or fictitious force that acts on objects in motion within a frame of reference that rotates with respect to an inertial frame. In a reference frame with clockwise rotation, the force acts to the ...

. The zone is of interest to biologist, geologists,

sedimentologists Sedimentology encompasses the study of modern sediments such as sand, silt, and clay, and the processes that result in their formation (erosion and weathering), transport, deposition and diagenesis. Sedimentologists apply their understanding of mo ...

oceanographers Oceanography (), also known as oceanology and ocean science, is the scientific study of the oceans. It is an Earth science, which covers a wide range of topics, including ecosystem dynamics; ocean currents, waves, and geophysical fluid dynami ...

, physicists, and engineers, as well as many other

scientific discipline The branches of science, also referred to as sciences, scientific fields or scientific disciplines, are commonly divided into three major groups: *Formal sciences: the study of formal systems, such as those under the branches of logic and mat ...

s. It is the area of interaction between the two environments and as such is important in many species' reproductive strategies, particularly larvae dispersal. The benthic boundary layer also contains nutrients important in fisheries, a wide array of microscopic life, a variety of suspended materials, and sharp energy gradients. It is also the sink for many anthropogenic substances released into the environment.

Life in the Deep Sea Benthic Boundary Layer

The benthic boundary layer (BBL) represents a few tens of meters of the water column directly above the sea floorJoan E. Cartes (1998
"Dynamics of the bathyal Benthic Boundary Layer in the northwestern Mediterranean: depth and temporal variations in macrofaunal–megafaunal communities and their possible connections within deep-sea trophic webs"
Progress in Oceanography 41: 111-139 and constitutes an important zone of biological activity in the ocean. It plays a vital role in the cycling of matter, and has been called the “endpoint” for sedimenting material, which fuels high metabolic rates for microbial populations. After passing through the BBL, this degraded material is either returned to the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

or mobilized into the

, where it may eventually become immobilized. With growing concern over the ultimate fate of matter in the ocean, knowledge of the complex biological processes in the

deep sea The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of 200 metres (656 feet) or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combin ...

BBL (deep-BBL) and how they affect future sedimentation and remineralization rates is valuable. In the deep sea (1800 m depth or greater), the BBL is noted as having a near homogenous temperature and salinity with periodic fluxes of detrital or

particulate organic matter Particulate organic matter (POM) is a fraction of total organic matter operationally defined as that which does not pass through a filter pore size that typically ranges in size from 0.053 to 2 millimeters. Particulate organic carbon (POC) is ...

(POM). This POM is strongly linked to seasonal variations in surface productivity and hydrodynamic conditions.Guidi-Guilvard, L. D., Thistle, D., Khripounoff, A., and S. Gasparini (2009
”Dynamics of benthic copepods and other meiofauna in the benthic boundary layer of the deep NW Mediterranean Sea”
Marine Ecology Progress Series 396: 181-195 Excluding

hydrothermal vents A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

, much of the deep sea benthos is

allochthonous River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.Angelier ...

, and the importance of bacteria for substrate conversion is paramount. While the supply of POM, or

marine snow In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...

, is relatively limited and inhibits species abundance, it sustains a complex yet understudied microbial loop that can maintain both meiofaunal and macrofaunal populations. In a study by Will Ritzrau (1996), it was determined that microbial activities were up to a factor of 7.5 higher in the BBL than in adjacent waters. While this study was completed between 100-400m depth, it could have implications for the deep-BBL. Presently, it is known that deep-BBL bacterial populations are able to support protozoan bacterivores like foraminifera and some metazoan zooplankton, which in turn can support larger organisms. Meiofauna and macrofauna found in the deep-BBL include:

copepod Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (inhabiting sea waters), some are benthos, benthic (living on the ocean floor) ...

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecol ...

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

isopod Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...

amphipod Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descr ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s and

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s, to name a few. These organisms ultimately play a vital role in the remineralization of matter and aid in breaking down POM that may eventually become permanent sediment. As the effects of anthropogenic forcing begin taking an even greater toll on marine processes, long-term studies are essential in determining the health and stability of the deep-BBL. Currently, several groups are employing cabled observatories (ALOHA Cabled Observatory,

Monterey Accelerated Research System Monterey Accelerated Research System (MARS) is a cabled-based observatory system below the surface of Monterey Bay, developed and managed by the Monterey Bay Aquarium Research Institute. The system, operational since November 10, 2008, incorporate ...

NEPTUNE Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...

VENUS Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

, and Liquid Jungle Lab (LJL) Panama- PLUTO) to work towards developing these much needed time-series.

References

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Sources

*The Benthic Boundary Layer, Transport Processes and Biogeochemistry. Edited by Bernard P. Boudreau and Bo Barker Jørgensen . February 2001, Oxford University Press. Oceanography Limnology