Temporal variation of chlorophyll-like pigment composition in sinking particles during the ice-covered season in Saroma-ko Lagoon

From 21 February to 23 March 1992, the temporal variation in the pigment composition of sinking particles was investigated under the ice of Saroma-ko Lagoon using high-performance liquid chromatography (HPLC). Chlorophyll a (chl a), early degradation products of chl a (chl d-1, −2, −3 and chlorophyllide a), and pheopigments (pheophytin a and pheophorbide a) were identified. Sinking fluxes of total pigment were rather constant from 21 February to 16 March after which they increased in all layers to reach a maximum of ca. 5 mg m−2 d−1. At all depths, the percentage of chl a in sinking particles was less than 50% until 16 March; after that it increased to 58.6 ± 7.38% concomitant with a temperature increase. The percentage of pheophorbide a in sinking material was high in samples collected before 16 March (30.6–48.7%) compared to those collected after 16 March (14.3–25.4%). Percentages of chlorophyllide a and chl d−1 varied from 0 to 7.2% in all layers during the study. Significant vertical variation was noticed in the pigment composition, suggesting that chl a could be degraded during the sinking process. Results of a similarity analysis on photosynthetic pigment composition of the sinking particles revealed four clusters, three for the sinking particles collected before 16 March and one for those collected after 16 March. The main features of each cluster were high pheophorbide a if the first (21–25 February) and third (9–16 March) clusters, higher chl d−2 in the second cluster (25 February–9 March) and high chl a and chl d−3 in the fourth cluster (16–23 March). These variations indicated that the degradation process of pigments in the water column depends on differences in the pigment source among the four periods. Our results indicated that senescent algal cells and fecal pellets were the source of most of the pigment flux during the low temperature period. With the temperature increase in early spring and the melting of bottom ice, an increased contribution of ice algae to sinking particles could have caused a major change in the pigment composition of the sinking material.