Diatom blooms and primary production in a channel ecosystem of central Patagonia

Abstract

ABSTRACT.Here we report on the seasonal productivity cycle at a fixed station in the Puyuhuapi Channel (44ºS, 73ºW), Chilean Patagonia. The analysis of in situ water column data and longer-term records of satellitederived surface ocean color (Chl-a) highlighted two contrasting seasons. A more productive period occurred between August and April, where depth-integrated gross primary production (GPP) estimates ranged from 0.1 to 2.9 g C m -2 d -1, and a shorter, less-productive season lasted from May to July with GPP ranging from 0.03 to. Diatoms of the genera Pseudo-nitzschia, Skeletonema and Chaetoceros dominated the phytoplankton, and showed a pronounced seasonality greatly influenced by prevailing environmental conditions. Warmer waters were associated with high concentrations of Pseudo-nitzschia spp., while high abundances of Skeletonema spp. and Chaetoceros spp. were associated with fresher silicate-rich waters. A marked Skeletonema spp. bloom characterized the onset of the productive season in August 2008, and with some exceptions, the highest levels of GPP (1.5 to 2.9 g C m -2 d -1) were measured when Skeletonema dominated the phytoplankton community. Reduced production (low GPP) was observed during periods of increased discharge from the Cisnes River, whereas the "spring" diatom bloom (or late winter bloom in Puyuhuapi Channel) observed during August 2008 coincided with a ~50% drop in the freshwater discharge. We therefore suggest that periods of intensive freshwater Input, that increase the silicic acid concentrations in the upper layers, provide ideal growing conditions for diatoms as the freshwater flow subsequently recedes. Principal component analysis (PCA) suggests that a decrease in salinity, increase in silicic acid concentration, and growth of Skeletonema spp. and Chaetoceros spp., are probably key factors in the annual cycle of GPP in Puyuhuapi Channel.

Scavenging crustacean fauna in the Chilean Patagonian Sea

“…Gross primary production and annual community respiration were 533 and 537 gC m 2 year −1 , respectively 24 , primary production was 800 mgC m 2 day −1 and there was a vertical flow of particulate organic carbon that doubled in spring (266 mgC m 2 day −1 ) compared to winter (168 mgC m 2 day −1 ) 25 . The depth-integrated gross primary production varied from the period of highest productivity from August to April (0.1 to 2.9 gC m 2 day −1 ) to a shorter period of lower productivity from May to July (0.03 to 0.3 gC m 2 day −1 ) 26 .…”

Spatiotemporal Distribution of Key Pelagic Microbes in a Seasonal Oxygen-Deficient Coastal Upwelling System of the Eastern South Pacific Ocean

“…In the study area, upwelling not only fertilizes the surface with high-nutrient content waters fueling primary and secondary productivity (e.g., Montero et al, 2007), but also develops a seasonal oxygen deficiency in the subsurface associated with Equatorial Subsurface Waters (ESSW) which was evident during our study (Ahumada and Chuecas, 1979;Sobarzo et al, 2007). Oxygen has been reported as a controlling factor of microbial community abundance (Eissler et al, 2010), structure (Aldunate et al, 2018), and biogeochemical active processes (Galán et al, 2014(Galán et al, , 2017Srain et al, 2020) in the study area.…”

“…The oceanographic dynamic in central-southern Chile along with the high solar radiation in spring-summer promotes a high primary productivity (Montero et al, 2007;Hernández et al, 2012) and faster remineralization rates (Daneri et al, 2000(Daneri et al, , 2012, that stimulate nitrification activity. Nitrification is a relevant process in the study area, reaching high net rates in the oxycline during the spring-summer (200-316 nmol L −1 d −1 ) compared with winter, c.a.…”

Linking Seasonal Reduction of Microbial Diversity to Increase in Winter Temperature of Waters of a Chilean Patagonia Fjord

“…This ecosystem is greatly influenced by rivers and the Patagonian Ice Fields (Pickard, 1971) and supports high rates of biological productivity and vertical export fluxes of carbon (Pantoja et al, 2005;González et al, 2010González et al, , 2011González et al, , 2013Montero et al, 2011Montero et al, , 2017a. The Patagonian fjord ecosystem as a whole is considered to represent a net sink of CO 2 (Torres et al, 2011;González et al, 2013) and of enhanced sedimentary burial of organic carbon (Sepúlveda et al, 2011;Smith et al, 2015).…”

“…The Patagonian fjord ecosystem as a whole is considered to represent a net sink of CO 2 (Torres et al, 2011;González et al, 2013) and of enhanced sedimentary burial of organic carbon (Sepúlveda et al, 2011;Smith et al, 2015). Previous studies within this coastal ecosystem have highlighted the role of winds, low-pressure systems, and freshwater discharge in driving cycles of biological productivity and composition of the phytoplankton community at seasonal and shorter time scales (Montero et al, 2011(Montero et al, , 2017a. Changes in the composition of microbial communities have also been related to seasonal variations in glacial melting (Gutiérrez et al, 2015).…”