Coastal Oceanography. Coastal Oceanography. Coastal Waters

Transcription

1 Coastal Oceanography Coastal Oceanography 95% of ocean life is in coastal waters (320 km from shore) Estuaries and wetlands are among most productive ecosystems on Earth Major shipping routes, oil and gas exploration, recreational activities take place in these waters Oceanography of coastal waters is markedly different than in open ocean. Coastal Waters Generally considered to be marine waters over the continental shelf Adjoining continents and island Area dependent on margin type Subduction or active margin, coastal waters are a narrow band Passive margins, coastal waters cover a larger area 1

2 Salinity and Temperature Shallower waters can be mixed rather thoroughly The Ekman layer can extend to the bottom seasonally and episodically Salinity isohaline Temperature isothermal Salinity River input decreases the salinity Isohaline at lower salinity than adjacent open ocean Conversely, strong haloclines persist where mixing is weaker Evaporative latitudes can cause coastal hypersalinity Coastal Salinity 2

3 Temperature In low latitudes, coastal waters can become hyperthermal No cooler water below to be upwelled Reflection of the sun off of the bottom sediments In high latitudes and in winter, waters do not get as cold as open ocean water before freezing Coastal Temperature Coastal Geostrophy Geostrophic currents move around the gyre centers 3

4 Coastal Geostrophy Coastal geostrophic currents are created by wind and runoff Coastal Geostrophy Winds can push fresh water runoff against the coast As fresh water continues to run off, water flows downhill on sloped surface Coriolis deflects this flow Coastal Geostrophic Currents Ephemeral Depend on wind and amount of runoff They can disappear periodically, seasonally 4

5 Estuaries Estuary partially enclosed body of water in which freshwater runoff dilutes salty ocean water River mouths Bays, inlets, gulfs Lagoons Origin of Estuaries Generally, result of sea level rise Coastal plain estuary Rising sea fills existing river valley drowned river valley Origin of Estuaries Fjord estuary Drowned glaciated valley Deeper, steeper due to glacial erosion Moraine deposits at mouth 5

6 Origin of Estuaries Bar-built estuary Created by formation of sandbar deposit Shallow, barrier island lagoons/bays Origin of Estuaries Tectonic estuary Formed by tectonic processes Faulting Folding Estuarine Mixing of Water Masses Stratified Little to no mixing of freshwater into saltwater Partially mixed Moderate mixing of salt and fresh water Fully mixed Isohaline zones Salt-wedge In regions of high runoff Inverse In hypersaline estuaries 6

7 Estuarine Salinity U.S. Estuaries Columbia River mouth Washington Oregon border Chesapeake Bay estuary drowned Susquehanna River mouth Mississippi River drowned river mouth Florida Bay modified bar mouth Columbia River Estuary Salt wedge estuary Balance between strong tides and high flow, with limited mixing 7

8 Columbia River Estuary Extensive dams provide irrigation and drinking water, electricity, and flood control Dams also have caused fairly extensive environmental changes Salmon run Nutrient delivery to coastal waters Sparsely populated watershed Chesapeake Bay Estuary Stratified drowned river mouth estuary Densely populated surroundings Highly seasonal stratification Asymmetric freshwater sources Chesapeake Bay Estuary Coriolis effect of water masses 8

9 Chesapeake Bay Estuary Strong stratification during spring freshwater flow prevents oxygen from getting to deep water Chesapeake Bay Estuary Coverage of anoxic waters and length of time of anoxic events has increased since the 1950 s. Why? Lagoons Bar-built estuaries Typical zonation Freshwater zone Brackish zone Saltwater zone Seasonality Evaporative seasons seawater flows in, salinity increases Rainy seasons water flows out, runoff decreases salinity 9

10 Laguna Madre North of Rio Grande River, between Texas and Mexico Semi-arid, hypersaline Little tidal exchange Inverse estuary Local Estuaries Lake Pontchartrain Rigolet s Pass attachment to ocean Bogue Falaya River Mississippi River Mississippi River Salt-wedge Bottom below sea level 250 feet Oak Street submarine coffer dam Coastal Wetlands Coastal wetlands Salt marsh Mangrove wetlands 10

11 Mangrove Wetlands Important nurseries for larval species Buffer to coastal erosion Use of nitrogen and phosphorous compounds that cause eutrophication Semi-enclosed Seas Mediterranean Sea sea half-encircled (medi-) by land (-terra) Mediterranean Sea 11

12 Mediterranean Desiccation Sea level decreased 150m during the last glacial maximum Only a low flow of Atlantic water entered the Mediterranean Other periods, evaporation has far exceeded inflow, drying out the Mediterranean completely and leaving thick salt deposits Noah s flood? Black Sea Flood Red Sea Silled basin like the Mediterranean Sea 12

13 Key Concepts Salinity and temperature controls in coastal waters Geostrophic currents in coastal waters Estuaries Origins Types Semi-enclosed seas and regional oceanography 13