( ( ( ( ( Deep ( ocean currents ) ) ( are ( generated ( ( ( ( by ( ( ( ( the sinking ) and ) upwelling ) ( of water ) ) ) , ) due ) ( to ( ( density differences ) ( driven ( by temperature ) ) ) ) ) ) ) ) and ) ( salinity ( -LRB- ( saltiness ( -RRB- contrasts ) ) ) ) ) . )
(ROOT (S (S (NP (JJ Deep) (NN ocean) (NNS currents)) (VP (VBP are) (VP (VBN generated) (PP (PP (IN by) (NP (NP (DT the) (VBG sinking) (CC and) (VBG upwelling)) (PP (IN of) (NP (NN water))))) (, ,) (RB due) (PP (TO to) (NP (NP (NN density) (NNS differences)) (VP (VBN driven) (PP (IN by) (NP (NN temperature)))))))))) (CC and) (S (ADVP (RB salinity)) (-LRB- -LRB-) (NP (NNS saltiness)) (-RRB- -RRB-) (VP (VBZ contrasts))) (. .)))
Deep ocean currents are generated by the sinking and upwelling of water, due to density differences driven by temperature and salinity (saltiness) contrasts.
(ROOT (S (NP (JJ Deep) (NNS currents)) (VP (VBP are) (VP (VBN caused) (PP (IN by) (NP (NP (NNS differences)) (PP (IN in) (NP (NN density))))) (PP (IN at) (NP (NP (DT the) (NN top) (CC and) (NN bottom)) (PP (IN of) (NP (DT the) (NN ocean))))))) (. .)))