Geology topics

Bruce Finney

Publications and source records attributed to Bruce Finney.

2 recordsLinked to original sources

USGS2013

Response of diatoms and silicoflagellates to climate change in the Santa Barbara Basin during the past 250 years and the rise of the toxic diatom Pseudo-nitzschia australis

Diatoms and silicoflagellate assemblages were examined in two year-increments of varved samples spanning the interval from 1748 through 2007 in Santa Barbara Basin (SBB) box core SBBC0806 to determine the timing and impact of possible 20th century warming on several different components of the plankton. Diatoms (Thalassionema nitzschioides =TN) and silicoflagellates (Distephanus speculum s.l. =DS) indicative of cooler waters and a shallow thermocline begin to decline in the 1920s and persistently compose a lower percentage of the assemblage in the SBB by about 1940. Prior to 1940, TN constituted on average ~30% of the Chaetoceros-free diatom sediment assemblage and DS on average ~36% of the silicoflagellate assemblage. Between 1940 and 1996 these relative abundances were ~20% (TN) and ~8% (DS). These results are consistent with results from planktonic foraminifera and radiolarians that indicate an influence of 20th century warming on marine ecosystems before most scientific observations began. Cooling of surface waters coincident with the one of the strongest La Niña events of the 20th century (and a return to negative PDO conditions) in late 1998 brought about a return to pre-1940 values of these cool water taxa (TN ~31%, DS ~25%). However, this recent regional cooling appears to have been accompanied by profound changes in the diatom assemblage. Pseudo-nitzschia australis, and Pseudo-nitzschia multiseries, diatom species associated with domoic acid, a neurotoxin that causes shellfish poisoning and marine mammal deaths, rapidly became dominant in the SBB sediment record at the time of the regional cooling (1999) and increased substantially in numbers as a bloom-forming taxon (relative to Chaetoceros spores) in 2003. Prior to 2003 diatom blooms recorded in the SBB sediment record consisted predominantly of Chaetoceros spores and less commonly of Rhizosolenia-related species (Neocalyptrella robusta and R. setigera). Fecal pellets dominated by valves of P. australis, however, were particularly abundant in both the 2003 and 2006 samples, coincident with recorded incidents of domoic acid increase and widespread shellfish poisoning in the SBB.

Quaternary International↗

USGS2009

Paleoceanography of the Gulf of Alaska during the past 15,000 years: Results from diatoms, silicoflagellates, and geochemistry

High-resolution records of diatoms, silicoflagellates, and geochemistry covering the past 15,000 years were studied in three cores from the Gulf of Alaska (GOA). Core EW0408-85JC in an oceanic setting on the Kayak Slope displays a paleoceanographic record similar to that at several locations on the California margin during deglaciation. Biologic productivity as reconstructed using geochemical and microfossil proxies increased abruptly during the Bølling–Alleröd (Bø–Al) warm interval (14.7–12.9 cal ka), declined during the Younger Dryas (YD) cold interval (12.9 to 11.7 cal kyr BP), and rose again during the earliest Holocene. At this site, the record after ~ 11 cal kyr BP is dominated by oceanic diatoms and silicoflagellates, with geochemical proxies displaying more subtle variation. Cores EW0408-66JC in the Yakobi Sea Valley near Cross Sound and EW0408-11JC in the Gulf of Esquibel contain an expanded, composite record along the southeast Alaskan margin. Core 66JC contains a detailed record of the Bø–Al and YD. Diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the Bø–Al but declined during the YD. Sea ice-related diatoms increased in abundance during the YD, indicating cooler, but less productive waters. The glacial to biogenic marine sediment transition in core 11JC occurs at 1280 cmbsf (centimeters below sea floor), probably representing rising sea level and deglaciation early in the Bø–Al. Freshwater and sea-ice related diatoms are common in the lower part of the core (Bø–Al and YD), but upwelling-related diatoms and silicoflagellates quickly increased in relative abundance up-core, dominating the record of the past 11,000 years. Low oxygen conditions in the bottom water as reconstructed using geochemical proxies (U and Mo concentration) were most intense between ~ 6.5 and 2.8 cal kyr BP, the beginning of which is coincident with increases in abundance of upwelling-related diatoms. The records from these three cores jointly thus made it possible to reconstruct paleoclimatic and paleoceanographic conditions at high northern Pacific latitudes during the last 15 kyr.

Alaska↗