For the world/embark below, the ocean is frozen for every season except Summer.
On the first day of Summer, it thaws. On the first day of Autumn, it freezes solid. The "Tropical Ocean" biome (most of the embark) will hold at 10,000'U up to and including the last day of Spring, and then on the first day of summer, the Temperature jumps to 10,003'U.
There are portions of the north & west
adjacent ocean that remain frozen year round, just to prove you can have frozen and thawed ocean in the same embark.
worldgenCreated in DF v0.40.12.
[WORLD_GEN]
[TITLE:FROZEN_OCEAN1]
[SEED:NVwg5I8ci8FxtNZ3LMXu]
[HISTORY_SEED:7muHisVaYNhwR27od9FO]
[NAME_SEED:xfyzPKtRLEtyi7h5ZLFS]
[CREATURE_SEED:GvEWGQOAUkG1KjIOu7RG]
[DIM:17:17]
[EMBARK_POINTS:5000]
[END_YEAR:100]
[BEAST_END_YEAR:100:-1]
[REVEAL_ALL_HISTORY:0]
[CULL_HISTORICAL_FIGURES:1]
[ELEVATION:1:350:0:0]
[RAINFALL:0:0:0:0]
[TEMPERATURE:-100:50:0:0]
[DRAINAGE:40:40:0:0]
[VOLCANISM:0:0:0:0]
[SAVAGERY:0:0:0:0]
[ELEVATION_FREQUENCY:2:8:0:0:0:2]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[POLE:NORTH]
[MINERAL_SCARCITY:1000]
[MEGABEAST_CAP:3]
[SEMIMEGABEAST_CAP:3]
[TITAN_NUMBER:1]
[TITAN_ATTACK_TRIGGER:40:0:0]
[DEMON_NUMBER:2]
[NIGHT_TROLL_NUMBER:0]
[BOGEYMAN_NUMBER:0]
[VAMPIRE_NUMBER:0]
[WEREBEAST_NUMBER:0]
[SECRET_NUMBER:0]
[REGIONAL_INTERACTION_NUMBER:0]
[DISTURBANCE_INTERACTION_NUMBER:0]
[EVIL_CLOUD_NUMBER:0]
[EVIL_RAIN_NUMBER:0]
[GENERATE_DIVINE_MATERIALS:0]
[GOOD_SQ_COUNTS:0:0:0]
[EVIL_SQ_COUNTS:0:0:0]
[PEAK_NUMBER_MIN:0]
[PARTIAL_OCEAN_EDGE_MIN:0]
[COMPLETE_OCEAN_EDGE_MIN:0]
[VOLCANO_MIN:0]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:999]
[RIVER_MINS:0:0]
[PERIODICALLY_ERODE_EXTREMES:0]
[OROGRAPHIC_PRECIPITATION:0]
[SUBREGION_MAX:5000]
[CAVERN_LAYER_COUNT:1]
[CAVERN_LAYER_OPENNESS_MIN:1]
[CAVERN_LAYER_OPENNESS_MAX:5]
[CAVERN_LAYER_PASSAGE_DENSITY_MIN:0]
[CAVERN_LAYER_PASSAGE_DENSITY_MAX:0]
[CAVERN_LAYER_WATER_MIN:51]
[CAVERN_LAYER_WATER_MAX:60]
[HAVE_BOTTOM_LAYER_1:1]
[HAVE_BOTTOM_LAYER_2:1]
[LEVELS_ABOVE_GROUND:10]
[LEVELS_ABOVE_LAYER_1:8]
[LEVELS_ABOVE_LAYER_2:2]
[LEVELS_ABOVE_LAYER_3:2]
[LEVELS_ABOVE_LAYER_4:2]
[LEVELS_ABOVE_LAYER_5:3]
[LEVELS_AT_BOTTOM:2]
[CAVE_MIN_SIZE:1]
[CAVE_MAX_SIZE:1]
[MOUNTAIN_CAVE_MIN:0]
[NON_MOUNTAIN_CAVE_MIN:0]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:2]
[TOTAL_CIV_POPULATION:2]
[SITE_CAP:10]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:0:0:0]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]
embark location