O

1. Obelia, 306

   1. reproduction, 320

2. Ocean currents, ecological relations of:

   1. animals, 858–869

   2. plants, 782–792

3. Oceanic environmental province, 275, 278

   1. animals, 821, 827

   2. plants, 763

4. Oceanographic vessels, 331–333

5. Oceans:

   1. areas, 13, 15

   2. boundaries of subdivisions, 12

   3. mean depths, 13, 15

   4. volumes, 13, 15

6. Oikopleura:

   1. feeding mechanism, 888

   2. systematic position, 312

7. Okhotsk Sea, 733

8. Oozes, ecological importance of, 278

9. Organic constituents in Sediments, 949–951, 983–986

10. Organic environment, 879

11. Organic matter:

    1. dissolved, utilization of, 911–913

    2. in sediments, 951

       1. chemical composition, 1010

       2. decrease with depth in deposit, 1016

       3. distribution, 1013–1017

       4. factors determining amounts, 1012–1013

       5. quantity, 1008–1010

       6. sources, 951, 1011

12. Organic production in the sea, 925–926

    1. commercial, 936–937

    2. cycle of organic matter in the sea, 926

    3. in different regions, 937–944

    4. phytoplankton, 927–934

    5. zooplankton, 934–936

13. Osmotic pressure, function of salinity and temperature, 66, 67

14. Osmotic relationships of body fluids:

    1. fresh-water animals, 269

    2. marine animals, 269, 271, 839

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― 1071 ―

15. Oxidation-reduction potential, 211, 212

    1. importance to accumulation of iron in sediments, 1032

    2. importance to accumulation of manganese in sediments, 1031

    3. in sediments, 995–997

16. Oxygen;

    1. as an environmental factor, 869–873, 903, 913, 917

    2. in organic matter in sediments, 1011

    3. production and consumption of, as index of organic production, 933–934

    4. production by plants, 767, 777, 933

17. Oxygen, dissolved:

    1. depletion in interstitial water, 995

    2. depletion in relation to nutrient content, 237

    3. determination, 187

    4. relation to pH distribution, 209

    5. solubility, 189–191

18. Oxygen consumption, bacterial, as a measure of organic carbon, 250

19. Oxygen content (see under specific geographic regions):

    1. oceanic deep-water, 746, 748, 752–754

20. Oxygen distribution (see under specific geographic regions):

    1. conditions for stationary, 161, 162

    2. related to deep-water circulation, 754

21. Oyashio, 721, 733

    1. meeting Kuroshio Extension, 722

22. Oysters, reproduction of, 316, 324, 846–847, 857