Inputs to shelf seas- an overview

Materials are introduced into coastal and shelf seas primarily through:

• rivers, • atmosphere, • groundwaters, • ice processes in polar seas

River inputs to coastal and shelf sea waters

Major player in hydrological cycleWater fluxes- function of basin size and precipitationPredominant route from land to ocean of water and suspended particulate matter (SPM)Regions of freshwater influence (ROFIs) (Amazon, Rhine); physical chemical and biological consequences

Temperature (left) and SPM signatures (right) of Rhine ROFI in the North Sea. Data collercted by satellite (c/o ESA)

Amount function of the erodibility of drainage basinGreater than 90% of riverine SPM is trapped in ocean marginsHigh SPM leads to extended fan structures and offshore sediment accretion

Suspended particulate matter inputs

Dissolved constituents

The coastal and estuarine “elemental filter”Association of elements with particles (scavenging) and biota, and particle removal to sediments

Estimates of removal of dissolved trace elements at ocean margins

Element Estuarine and biological removalas % of estimated river and

atmospheric inputAs (arsenic) 2Zn (zinc) 37Al (aluminium) 11Fe (iron) 47Mn (manganese) 44

Martin and Windom (1991) In: Ocean margin processes in Global Change

Atmospheric inputs to shelf seasAs most particles from terrigenous sources, major inputs close to land (order of 50% of total atmospheric inputs to oceans is in margins)Important input route for volatile pollutants

Dry deposition direct fallout of particles to sea surface- difficult to quantifydissolution of elements from particles on hitting the sea

Rainfall – wet deposition washes out particles and some material already in solution rain can dissolve fraction of elements on particles

Groundwater (GW) Inputs

Springs and seeps are features of many coastal systems e.g. springs observed coasts of, Yucatan peninsula, Western Australia, Europe etc.

Important chemical changes can occur in GW (“iron curtain”) that may modify chemical fluxes (Charette and Sholkovitz, JGR)

Natural radioisotopes (Ra, Rn isotopes) and some stable elements (e.g. Ba) are being used as tracers

We know very little about the magnitude and impact of such GW systems (difficult to measure and lack of appreciation)

Slow seepage may be more important in volume of water introduced and associated constituents

Polar seas

Ice transport- “drop-stones” and glacial erosion/melt water

Benthic exchanges

Sediments ultimate long-term repository (“sink”) for elements and particles introduced into marine watersBoth active recycling of many elements at benthic interface and...Longer time-scale release of materials into water columnExample of fluxes of nutrients from sediments in the North Sea- rivers major input of nutrient but estimated 10-26% of phosphorus needed for net primary production can be from sediments

Note that coastal seas may be a source of some gases

such as DMS (dimethyl sulphide):

Precursor to sulphate particles in atmosphere (responsible for albedo and partial control of surface temperature of planet)

Natural source of S acid components in atmosphere, as well as fuel combustion (power stations).

Water flows, and exchange with the open ocean fundamental to understanding of biological geochemical geological processes in continental and shelf sea systems e.g. upwelling, and advection on & off shelf

See the introduction to physical processes by Dr Sharples