Ocean Circulation 1 - Dr David Evans

Question 1

MEridonial ocean circulation

Answer 1

A global ocean circulation system which connects the worlds ocean. The circulation is driven by both wind and variations in water density.

THERMOHALINE CIRCULATION - this term does not include the wind as a factor

Question 2

Why is the Meridonial circulation important

Answer 2

• Carries heat from the tropical Atlantic to higher latitudes.
• Ventilates the deep ocean
• Redistributes nutrients, oxygen, carbon, pH

Question 3

units for :

Sea Water density

Answer 3

ρ (rho) kg m-3
but most commonly used is the σ (sigma) which is
(ρ – 1000) kg m-3

Question 4

describe the distribution of density across the globe

Answer 4

High density in the Poles due to the cold nature of the water

High density in the mediteranian due to the high salinity- there is only a very narrow dea near jaboltra.

Low density near the tropics where there is high evaporation and precipitation

higher salinity in Atlanti than pacific due to higher precipitation and more water f entering from rivers

Question 5

seawater density definition

Answer 5

(ρ) typically ranges from 1.025-1.028 g cm-3

a function of salinity and POTENTIAL temperature (theta ϴ)

Question 6

potential temperature

Answer 6

the IN SITU temperature corrected for the effects of compression (pressure)

Question 7

Isopycnals

Answer 7

Contours of equal density

Question 8

North Atlantic Deep Water Formaiton

Answer 8

1. Forms in the Labrador Sea (forms upper NADW) and the seas between Iceland, Greenland and Norway (forms lower NADW).
2. North Atlantic Drift Current carries warm salty Gulf Stream water south of Iceland, into Nordic Sea and then further north to the Arctic.
3. Cold fresh polar surface water flows south through the Fram Strait and mixes with the warmer salty Atlantic Water in the Nordic Seas. Heat from the Atlantic water is released to the atmosphere and the mixed water is dense enough to sink.
4. NADW forms intermittently in chimneys which are up to 100 km in diameter. The sinking water must overflow the shallow ridge (300-1000 m deep) running from Greenland to Scotland

.

Question 9

name the way in which NADW is tracked

Answer 9

Two arrays of deployed instuments - TEmp, salinity and current velocity:

1. RAPID (26°N) runs 2001-2020
2. OSNAP (North Atlantic sub polar gyre) runs 2014 - 2018

Question 10

Pattern in anomalies regarding the circulation of the waters

Answer 10

in the last decade there has been a drop in the rate of movement of the water going north and also going south

Question 11

how did the ocean circulation relate to 2010

Answer 11

Uk froze over in 2010 and snow was everywhere as the flow northward of surface waters and flow southward of deep waters reduced, meaning less warm water was provided to the uk in the atlantic, so was colder.

Question 12

Antarctiv Bottom Water formation (AABW)

Answer 12

Antarctic Bottom water (AABW, in green) forms at multiple sites (purple arrows) and migrates out of the Antarctic region (blue arrows).
AABW is very cold and quite saline.

mainly forms in polynyas (ice free areas of sea in the ice cover):

Question 13

POLYNYAS

Answer 13

Antarctic bottom water forms at multiple locations around Antarctic due to cooling and ice formation in polynyas (areas of ice free water in the ice cover). It forms around the continental shelf and in deeper waters of the Antarctic Circumpolar current. Coastal polynyas occur where the wind drives newly formed ice off shore creating areas of open ocean 50-100 km wide. These act as sea ice factories. The continual freezing cools the surrounding water and increases it’s salinity. This is cooling due to latent heat of freezing (so they are called latent polynyas). Seawater at the ocean surface stays liquid even at temperatures approaching -2ºC because of its high salt content. The sinking water circulates over the continental shelf and then forms deep water. Open ocean polynyas occur far from the coast (over the continetal shelf or in deeper water). Here heat is lost from the water by convection/conduction (cooling is by sensible heat loss and they are called sensible polynyas) and the cooled water sinks. Open ocean polynyas are kept open by the upwelling of warm waters. Most deep water remains trapped in the deep basins around the Antarctic but some escapes and contributes to the Atlantic, Pacific and Indian ocean basins