Exam revision chapter 3

how have rivers and sea interactions shaped landscapes

how have rivers and sea interactions shaped landscapes

rivers are a major source and have a massive influence the chemical constituents of the ocean come from rivers there are complex and finely balanced interactions between climate, geology, topography, chemistry and biological control on the natural flow of water, sediment and nutrients which shapes river sea ecosystems

what are the processes and exchanges influencing nutrient distributions in estuaries

weathering industry sewage agriculture river input atmosphere: dry and wet deposition tidal exchange groundwater exchange resuspension bioirrigation biology: phyto, zoo, bacteria

river test and itchen inputs

test: industrially, commercial port itchen: agricultural runoff

how are rivers a major source of chemical elements to the ocean

regulate their own chemistry and therefore regulate primary production - plankton need nutrients from rivers

what does chemical weathering regulate

concentration of atmospheric CO2 over long time scales there are feedbacks between weathering and climate

silicate weathering

atmospheric CO2 goes to silicate weathering calcium silicate is turned into bicarbonate organisms e.g. diatoms use CaCO3 for shells and protection this flows through rivers to the ocean and buried in the sediments (locked away - CO2 storage) subduction lifts it from the sediments into mantle, degassing and metamorphism then into the atmosphere

what are the types of atmospheric inputs

dry deposition: aerosols - direct fallout of particles to sea surface and subsequent dissolution wet deposition: rain - washes out particles so some material dissolves coastal deposition: from land

what are high inputs from land

dust generated by wind erosion - desert to Atlantic, removed crops leaves dust and blows to river sea salt anthropogenic: power plant emissions, car exhausts, fertiliser volatilisation, other industrial emissions

what are the N inputs to coastal seas

mainly derived from combustion sources (acid rain) releasing NO/NO2 to the atmosphere which forms HNO3 or NO3- agricultural emissions release principally NH3 dispersed throughout the coastal zone - atmosphere is broad so fluxes variable (not a point source like rivers) fluxes variable in space and time but contribute 20-30% of total land-based N inputs e.g. to southern North sea and north atlantic shelf - seasonality has different impacts no N atmospheric inputs in the Southern Ocean

how to atmospheric sample in Bermuda

aerosol tower samples the air instruments: rain samplers, filter towers, measure pollutants from US, Saharan Dust - iron supply sector field so can only sample when wind blows from the ocean power supplied from containers differences in samples seasonally - high Fe in summer due to dust plume, low in April

what are the inputs of toxic metals

lead concentrations high in surface waters due to combustion of leaded petrol mercury from atmospheric deposition - volatile element as mainly deposited as Hg2+ in rain, global atmospheric burden increased due to humans atmospheric lead decreased but still high in ocean as takes time reducing atmospheric inputs reduces inputs to coastal regions

what is a key source of trace gases to the ocean

estuaries and coastal seas directly or indirectly biological in origin

where does methane come from

mainly sediments but may be produced at pycnocline - region of high productivity and reduced O2 - O2 min zones are always coastal produced by anaerobic microbial processes - sulphur smelling sediment - productive oxygenated surface waters on coastal shelves supersaturated with CH4 (methane paradox) 3% contribution of total CH4 emissions or 10% of natural CH4 emissions from coastal waters - no account of bubble fluxes

impact of methane on the atmosphere and climate

20x more impact on climate than CO2 - natural and produced in biological origin microbes and bacteria in anoxic estuarine mixing, methane escapes to atmosphere - high to low conc gradient methane in equilibrium with atmosphere

ship plume inputs of methane

large increase in pollution from ship's fuel decreased after law for reduction in ship SO2 emissions - reduce atmospheric pollution decreases marine pollution

where does N2O flux come from

continental shelves and estuaries and contributes to total oceanic emissions by-product of microbial nitrification (oxidation of ammonia to nitrate) and intermediate during microbial denitrification (take up nitrate)

where does DMS flux come from

dimethylsulphide natural gas into the trophosphere produced by phagocytes, coccolithophores and dinoflagellates fluxes higher in summer (phyto bloom) estuarine and coastal waters contribute lots to total global DMS emissions

how does DMS affect temperature and climate

oxidised in the troposphere contributing to atmospheric acidity and formation of cloud concentration nuclei

what is submarine groundwater discharge

direct flow of groundwater into the ocean mixture of fresh and saline water - wide range in salinity occurs as a slow diffuse flow but can be found as large point sources in certain terrains historically insignificant but now know has significant impact on biogeochemical cycling

fresh pore waters in SGD

shallower lots of water circulation in water table more fresh since water from rain

saline pore waters in SGD

becomes hyper saline as takes more dissolved solids out of water

how is composition of SGD modified

by chemical reactions in the aquifer (atmosphere) e.g. at discharge sites, depending on location, can see white therefore more calcite from eroded rocks at depths

meteoric waters: driving forces and contributing factors

freshwater driving force: hydraulic gradient - occurs when tide goes out contributing: topography, transmissivity, precipitation, evaoptranspiration

recirculated seawater: driving forces and contributing factors

salt water driving force: hydraulic gradient, tidal pumping, wave set-up contributing: tidal range, period, frequency, wind force and direction

connate water: driving forces and contributing factors

very salty (>36) driving force: density, thermal gradient contributing: geology, geothermal heating

how to detect and quantify SGD

infrared imaging: at high lats, SGD is warm relative to ocean (land warmer than sea), at low lats is cooler direct measurements: seepage meters - from space can see temp sources tracer techniques: works if know where SGD is, natural, usually radionuclides (uranium and thorium decay series), artificial (dyes) detect: seawater goes into sediment, occurs at low tide, get discharge when water out of sediment at high tide

characteristics of Ra tracers

radium - chemical tracer 4 naturally occurring isotopes that decay at different times half-lives span a range of time scales 224Ra: 3.66d, 223Ra: 11.6d, 228Ra: 5.75y, 226Ra: 1600y

how to use 226Ra as a tracer

longest half life so easiest to measure (longest decay) concentrations/activities high in coastal aquifers (water table) - derived from radioactive decay of 228U in aquifer rocks concentration low in seawater so high levels in coastal ocean = large SGD fluxes to coastal ocean less effective tracer for fresh SGD as Ra is bound to particles in freshwater

example: SGD in the Med

SGD is 16x larger than river input large coastline relative to area lots of land therefore lots of SGD

what are the water and chemical fluxes in SGD

water flux from SGD: 0.3-16% of global river flow (most 6-10%) total dissolved salts: way of measuring salinity, 50% contributed concentrations of nutrients, trace metals, organic carbon, methane and CO2 may be considerably higher in SGDs than seawater and freshwater

what are the chemical reactions in the subterranean estuary

oxidation of organic C adds CO2 and -> calcite dissolution high levels of nutrients due to water-rock interactions (P) and anthropogenic inputs (N,P) removal of nitrate due to denitrification in low oxygen groundwaters removal of dissolved iron at freshwater-saltwater interface and scavenging of other components (P)

different inputs from sources

rivers: 1.2-1.5 x10^13 mol/yr groundwater contribution: 26-50%

what are glacial inputs to polar shelf seas

meltwaters: supply iron in solution and as nanoparticles (bioavailable), not directly discharged to ocean inputs of Fe from melting of base of glaciers is a sufficient fuel of productive and long lasting phyto blooms meltwaters also observed in Arctic beneath ice sheet breakdown of iron oxyhydroxides by microbes under anoxic conditions could enhance iron concentrations

benthic source characteristics

sediments are long term repository sinks for elements in oceans there is active recycling of elements at the benthic interface and long timescale release of material into the water column

what are benthic sources to the marine environment

delivery of dissolved iron from coastal and shelf-seas could account of 50% of global Fe to oceans release of P from Fe oxides and organic material under anoxic conditions - 10-26% of P needed for primary production