D*'ep-Sea Re~earch. Vol 3~4.No 2. pp 243-Zt~. lqqt (119~114~/ql $3(I) + I)IM) Pnntcd in Gr~at Brttmrt ~ l.'~! Pergamon Pr¢~,.',, pie Distribution of phytoplankton pigments in the North Pacific Ocean in relation to physical and optical variability MICHAEL E. ONDRUSEK,*~"ROBERTR. BIDIGARE,*t STEPHENT. SWEET,* DEBRA A. DEFREITAS* and JAMES M. BROOKS* (Received 9 January 19"~): in revised forrn 25 Ju/y 1994): accepted 29 August 1990) Abstract--To investigate phytoplankton distributions in the North Pacific Ocean, samples of suspended particulate material were collected from the upper 3(X)m during two cruises in It~85for detailed analysis of algal pigments by high-performance liquid chromatography (HPLC). Trans- pacific Leg [ along 24°N in April and May, crossed three prominent hydrographic features: the California Coastal Current. the North Pacific Central Gyre and the Kuroshio Current. Transpacific Leg II. along 47"N in August and September. crossed the Kurt+shioextension, the Subarctic Gyre and the North Pacific Current. Individual pigments were partitioned vertically in the water cohtnm. showing distinct spatial patterns across the Pacific Ocean which reflected the large-scale circu- lation. Vertical distributions of phytoplankton pigments displayed c~msistent patterns over spatial scales of thousands of kilometers. In near-surface, nitrate-rich waters, fueoxanthin was the dominant carotenoid. In nitrate-poor st, rfaee waters, zcaxanthin w;is the dominant caroten~id at the surface, and 19'-hcxanoyh)xyfucoxanthin and chlorophyll h concentrations wcrc elevated near the base of the cuphotic zone. Phaeopigmcnt conCClltraliollS grc~itcr than ;I few tens of nanogranls per liter were never encountered. Based on Principal Ct'qnponcnt Analysis, stations clustered into three gener;,l pigment categories which followed specific hydrographic characteristics of oligotro- phic. highly productive and transitional regions. INTRODUCrlON Till.: North Pacific Central Gyre is a subtropical anticyclonic circulation system that is remarkably homogeneous for horizontal spatial scales of hundreds of kilometers (Fig. 1). Within the boundaries of the Gyre, chlorophyll a concentrations are generally low at the surface and increase with depth to form a narrow, horizontal layer of maximum concen- tration. This layer is often coincident with the base of the euphoric zone (approximately I% of surface irradiance) and extends over most of the Central Pacitic (VENR|CK et al., 1973; KJt.:I:ER etal. 1976; CULLeN and EPPLEY, 1981 ; TAKA|IAS|I| and Hokl, 1984). This deep chlorophyll maximum layer (DCML) typically lies between the warm, nutrient-depleted surface waters and the colder, nutrient-rich waters found below. By contrast, at the boundaries of the Central Gyre, there are relatively high chlorophyll a concentrations in near-surface waters (ANDERSON, 1969; SAtJO et at., 1969; TAKAItAS|I| et al., 1972; PEI,AE.:Z and McGowAN, 1986). °Geochcnfical & Environmental Rese;.rch Group, Department of Oceanography, Texas A&M University. College Station, TX 77,v~43.U.S.A. 1'Present address: Dep;.rtment of Oceanography. 10<l(I Pope Road, University of Hawaii. Flonolulu. 111%N22. U.S.A. 243