Chapter 3 Chemical and physical features of seawater and the world ocean Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

The waters of the ocean

The importance: more than 85% of most organism is composed of water -- more than 95% in jellyfish

The Unique Nature of Pure Water

The Three States of Water

Seawater becomes denser as it cools until it freeze ? Ice is less dense than liquid water ?

Water as a solvent Can dissolve more things than any other natural substance – universal solvent Especially good at dissolve salt -- What is salt ? Made up many ions

Sources of materials that make up seawater; rock weathering (major), hydrothermal vent release, (3) volcano input

Composition of seawater Major ions Minor ions

Composition of seawater 6 major ions, make up > 98% of dissolved ions: sodium and chloride make up 85% of dissolved ions.

Definition of salinity Total amount of salt dissolved in seawater range from 33 to 37‰, average 35‰; extremely salt in Red Sea; 40‰, and extremely fresh in Baltic Sea: 7‰ in surface depend on the balance of evaporation, precipitation and freezing.

Variation of water in ocean Water is removed by evaporation (major) and freezing Water is added by precipitation, snow (major) and melting of glaciers and polar ice

Measurement of salinity evaporation of salt water, electrical conductivity; Unit: psu (practical salinity unit) ocean is chemically well-mix; changed by variation of freshwater

Character of seawater rule of constant proportion

Density of seawater is influenced by ….. temperature and salinity Which is densier in the colder and more salty water

Temperature of the open ocean ranges from -2 to 30℃ -- measured by (1) the thermometer- Niskin bottle *along with the salinity sampling bottle

vertical temperature profile

-- Niskin bottles

(2) CTD (conductivity-temperature-depth meter) and XBTs (expandable bathythermograph meter); measure temperature, not salinity profile; and disposal

(3) Satellte imagine -- also used for the measurement of photosynthetic pigment concentration

Dissolved gases higher in the polar waters dissolved oxygen and dissolved CO2

dissolved oxygen 0-8 ml/l—more between 4-6 ml/l compared to air about 21 ml/l affected by photosynthesis and respiration

Dissolved CO2 react chemically when dissolved more than 80% in ocean compare to 0.04% in air

Transparency measured by the Secchi disk concentration of suspended particles measured by the Secchi disk

Why the ocean is blue in color ?

Pressure 1 atm (14.7 pound per square inch or 1 psi) at the surface. Seawater is densier than the air; marine organisms are under much more pressure than those on land

Underwater pressure increase 1 atm with the increase of 10 m in water depth

-- Reverse effect of decrease water pressure

Ocean circulation Marine organisms and their habitat, Profound effect: Marine organisms and their habitat, Earth climate; thus all habitats on land

Circulation pattern is determined by the wind and Coriolis forces Surface Circulation Circulation pattern is determined by the wind and Coriolis forces

Coliolis effects

Wind pattern: formation mechanism

Wind pattern Trade wind (between 30˚and equator), westerlies (between 30 and 60˚), polar easterlies Transition zone or boundary between two major wind bends have very light and changeable wind patterns

Eckman Spiral and Eckman transport -- Eckman layer down to Few hundred meters

-- Net transport to the right of the wind (North hemisphere) -- Major surface current is driven by the wind: move at an angle of 45˚ to the right (north hemisphere) -- Net transport to the right of the wind (North hemisphere)

Wind pattern and Coriolis force produce the gyre -- influence the distribution of temperature, thus marine organisms

Surface temperature is higher on the western side of the ocean than the eastern side -- coral reef is more abundant on the western side and kelp bed is more abundant on the east side

-- El Niño -- On the continental shelf, currents are strongly effected by the bottom, shape of the coastline and tide -- El Niño

wind and Current direction

海平面 洋流 西岸 東岸 湧升流

聖嬰與反聖嬰現象 「El Niño」意為「男嬰」或「聖嬰」 相反的現象稱為「La Niña」意為「女嬰」， 或譯作「反聖嬰」 正常狀況下，北半球赤道附近的東北貿易風 帶動海水自東向西流，此處海洋深處之低溫 海水會上湧來補充西行流走之洋流 此“湧升流”含豐富養分，因此會形成重要 的漁場，而海鳥亦隨魚群湧現而聚集，海鳥 排泄物則成為當地農業的主要肥料來源

聖嬰現象 在「聖嬰」現象發生期間，熱帶東風帶會減弱， 甚至轉為西風帶 東岸 西岸 洋流 沉降流

聖嬰現象 東太平洋抑制了該區深處之低溫海水上湧 群聚集數量減少，海鳥出現之數量亦銳減 「聖嬰」現象約每二年至七年發生一次，前 後可達一年半到二年之久 西太平洋區因乾旱會衍生出火災 ，而東太 平洋區受產生水患，造成上億美元的損失

反聖嬰現象 聖嬰現象像鐘擺一樣，會逐漸回復正常，但有時在回復過 程卻擺過了頭 造成盛行東風更強，東太平洋的表水溫反而更低，就形成 了反聖嬰現象

反聖嬰現象 仍以熱帶太平洋地區較顯著 位於西太平洋地區的印尼、澳洲等國 家，易有水災 而東太平洋區則會乾旱無雨

ENSO 聖嬰與反聖嬰現象常伴隨大氣的氣壓場有如 蹺蹺板式的東西振盪 氣象界通常以南太平洋東部之大溪地和西部 澳洲達爾文二地間氣壓場的差異值為指標來 顯示，並名為「南方振盪」(Southern Oscillation) 「聖嬰」和「南方振盪」此一相伴相生之大 氣、海洋變化現象，就取二個名詞之字首 合稱之

Thermohaline Circulation and the Great Ocean Conveyor

Ocean is usually stratified with the densest water (cold and heavy) on the bottom and the least dense (light and warm) at the surface

-- two factors: temperature and salinity -- The more stable the water column is and the harder it is to mix vertically

Thermohaline circulation the ocean is made of three primary layers: (a). the warm surface layer; about 100 to 200 m depth; mixed by wind, wave and tide. (b). intermediate thermocline layer, down to 1500 m. (C). deep cold bottom layer，below 1500 m

Stability and overturn Stable Overturn

Overturn (or downwelling) Mechanism: when the surface water becomes more dense than the water below; surface water sink (descend) displacing the less denser water below it Overturn usually occurs in temperature and polar regions during the winter when the surface water cools

Thermohaline circulation

Mechanism surface ocean salinity changed by the processes of precipitation, evaporation, and freezing surface temperature changed of heat with the air Once surface water; salinity and temperature do not change– water mass formed

Thermohaline circulation

The Great Ocean Conveyor

The Great Ocean Conveyor Take about 4000 years to complete the tour Bring dissolved oxygen to the deep sea

Wave -- Wave begin to form as soon as the wind starts to blow

Wave characters; crest, trough, height, wavelength, and period

Water particle motion in wave

Seas, swell, and surf

Tides Tide are caused by a combination of the gravity of the sun and moon ad the centrifugal force results from the rotation of earth, sun and moon

-- It takes 24 hours and 50 minutes to catch-up the mon

Tides Spring tide Neap tide Semidiurnal tide (most places)

(Coast of Antarctic and (west coast of US and Canada) (Coast of Antarctic and part of Gulf of Mexico, Caribbean and Pacific

-- Influential factors; land, weather pattern