Question: in one word what is the primarily driving force for deep currents
[{'answer': 'convection', 'provenance': [{'wikipedia_id': '387457', 'title': 'Thermohaline circulation', 'start_paragraph_id': 7, 'start_character': 501, 'end_paragraph_id': 7, 'end_character': 511, 'bleu_score': 1.0, 'section': 'Section::::Overview.\n'}]}, {'provenance': [{'wikipedia_id': '387457', 'title': 'Thermohaline circulation', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 952, 'bleu_score': 0.9700126434602441, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5718143482579648484}, 'section': 'Section::::Overview.\n'}]}]