ATOC 5051 INTRODUCTION TO PHYSICAL OCEANOGRAPHY

Lecture 2 Ocean basins and relation to climate Learning objectives: (1)  What are the similarities and differences

among different ocean basins? (2) How does each ocean basin geometry affect ocean circulation & climate, and why?

The world’s oceans

Ocean

Beach

1. Common feature of ocean basins

Continental Rise: gentler slope than continental slope

Description of ocean basins

Abyssal Plain

Open ccean Land

Shelf: 7.4% 0-200m; Slope+Rise: 15.9% 200-3000m; Abyssal Plain: 76.7%, >3000m.

Ocean basin: common features

Topography

(ridges and trenches)

The deepest trench in the world’s oceans: The Mariana trench in the western Pacific, ~deepest: 11km (Challenger deep). 2,550 km long; Average: 69km wide

Mid-Atlantic ridge - SW Indian Ridge - Central Indian Ridge - Southeast Indian Ridge - Pacific Antarctic Ridge - East Pacific Rise.

Interocean ridges:(could affect the flow of deep water)

Mid-Atlantic ridge; SW Indian Ridge; Central Indian Ridge; Southeast Indian Ridge; Pacific Antarctic Ridge; East Pacific Rise.

2. Differences in ocean basins & effects on circulation and climate

The Pacific The Atlantic The Indian Ocean The Arctic Ocean (Some books list “The Southern Ocean” as an independent ocean. Here, it is included in the first 3 major oceans.)

The Pacific

Pacific

Atlantic Indian

Malacca Panama SCS

OKH

Ross sea Weddell

The Pacific Ocean Zonally: 20,000km Meridional extent: over 15,000km; Area: 178x106km2 with all adjacent seas 40% of world’s Oceans ~ area of all continents

Arctic

The Pacific

•  The largest. In the tropics, •  zonally: spans 20,000km (from Malacca

strait to Panama); •  Meridional extent: Bering Strait to

Antarctic, over 15,000km; •  Area: 178x106km2 with all adjacent seas;

Represent 40% of the world ocean surface (equivalent to the area of all continents)

•  Without southern part, 147x106km2, twice of the Indian Ocean.

The Pacific: air-sea interaction

•  Vast ocean: strong air-sea coupling (small continental monsoon effect); El Nino-Southern Oscillation (ENSO) - global climate mode of variability, global impact; also Interdecadal Pacific Oscillation;

•  Mean depth, 4270m; •  No DEEP water source (away from its S. Ocean); •  Ridges: Pacific-Antarctic, East Pacific Rise,

Emperor Hawaiian Seamounts Ridge, Chile Rise, Nazca Ridge.

•  Main adjacent seas: South China Sea, East China Sea, Sea of Japan, Sea of Okhotsk, Bering Sea,etc.

The Atlantic

The Atlantic •  Different from the Pacific: the Atlantic

extends both into the Arctic and Antarctic Region; full meridional extent;

•  Zonal: largest extent (Gulf of Mexico-NW Africa), 8300km;

•  Area: 106x106km2; •  Mean depth: 3300m; •  Ridges: Mid-Atlantic.

The Atlantic •  The full meridional extent: favors DEEP

Water Formation (since the far northern latitude is exposed to the cold air from continent – cool the ocean; plus sea ice formation – ejects salt; both of which increase surface water density) - important for global thermohaline circulation (thermo-thermal-temperature; haline: salinity; board demo)

•  It has the largest number of adjacent seas. A major adjacent sea - the Mediterranean Sea, produces the Mediterranean water mass.

•  Close to continents: both monsoon and air-sea interaction are important in shaping the climate.

The Indian Ocean & inter-ocean connections

30N

Indonesian Throughflow (ITF) Supergyre

Agulhas current

The Atlantic

Pacific

The Indian Ocean

•  Smallest among the three. Meridional extent: 9600km (Antarctic - inner Bay of Bengal);

•  Zonal: 7800km (S. Africa - W. Australia) •  Area: 74x106km2; •  Interesting feature: connecting to the Pacific via

the Indonesian Throughflow (and through south of Australia-the super gyre), and to the Atlantic via the Agulhas Current;

The Indian Ocean •  North, bounded by Asian subcontinents;

seasonally-reversing monsoons are major feature in its climate; air-sea interaction is recently found to be also important, especially for the Indian Ocean Dipole mode;

•  Another interesting feature: northern boundary is in the “tropics”. => waves forced remotely by the equatorial winds can influence northern coast of the Indian Ocean.

•  Mean depth: 3800m; Ridges: Southwest Indian, Central Indian, Southeast Indian, Ninety East Ridge.

The Arctic Ocean

The Arctic Ocean •  Covers the arctic region - smallest, shallow. •  Area: 14x106km2 (2USA); •  Sea ice covered region varies with season; •  Major connections with the Atlantic: ~1700km

wide opening from Greenland across to Iceland, Faroe Islands and Scotland; Minor opening: Canadian Archipelago.

•  Connection with the Pacific: Bering Strait. Narrow, shallow (45m deep and 85km wide).

The Arctic Ocean & inter-ocean connection •  Sea ice export to the North Atlantic; its melting

and freezing affect deep water formation and thus global thermohaline circulation; sea ice concentration area – affects albedo – climate;

•  Atlantic warm water can also flows to the Arctic, affects sea ice formation/melting.

•  Mean depth: central basins: 3600-3800m. Separate into a few basins by Ridges.

•  Major Ridges: Alpha and Mendeleyev Ridge, Lomonossov Ridge, and the Arctic Mid-Ocean Ridge (Nansen Ridge).

Summary •  The world’s oceans have commons features. What are they? •  The world’s oceans: the Pacific, Atlantic, Indian and Arctic •  The Pacific: largest in size, climate mode (why?) •  The Atlantic: Largest meridional extent, thermohaline circulation

– affecting global climate; •  The Indian Ocean: most region located in the tropics – northern

boundary: Asian land – monsoon (why?) •  The Arctic Ocean: mostly covered by sea ice; sea ice

concentration – affect albedo & air-sea heat exchange; laterally, it exchanges water& ice with the Atlantic and the Pacific.