Benthic foraminifera in Neogene laminated diatom ooze of ODP Hole 138-844C

Several widely correlatable intervals of laminated Thalassiothrix diatom mat deposits occur in Neogene sediments recovered from the eastern equatorial Pacific Ocean. The presence of laminated sediments in extensive areas of the deep open ocean floor raises fundamental questions concerning the cause of preservation of the laminations and the nature of the benthic environment during episodes of mat deposition. Traditional explanations for the preservation of laminations have centered on restriction of dissolved oxygen. Studies of benthic foraminifers through the laminated intervals show no evidence for an increase in absolute or relative abundance of species characteristic of a low oxygen environment, but rather a decrease in relative abundance of infaunal forms attesting to the impenetrability of the diatom meshwork formed by the interlocking Thalassiothrix frustules. These results support evidence from coring of the high tensile strength of the Thalassiothrix laminations suggesting that the diatom meshwork was of sufficient tensile strength and impenetrability to suppress infaunal benthic activity. Comparison of the relative abundances of foraminifers in the enclosing ôbackgroundö sediment of foraminifer nannofossil ooze and the laminated diatom oozes shows that some epifaunal species (e.g., Cibicides spp.) increase in relative abundance within the laminated sediment, whereas others (e.g., Epistominella exigua) show a marked decrease in relative abundance. Other species show more complex changes in abundance related to the occurrence of the laminated sediments, which may indicate a combination of controls that include the physical nature of the substrate and the amount of organic flux.

Radiocarbon ages, diatom abundance and laminae description of sediment core MD03-2597

Laminated sediments are unique archives of palaeoenvironmental and palaeoceanographic conditions, recording changes on seasonal and interannual timescales. Diatom-rich laminated marine sediments are examined from Dumont d'Urville Trough, East Antarctic Margin, to determine changes in environmental conditions on the continental shelf from 1136 to 3122 cal. yr BP. Scanning electron microscope backscattered electron imagery (BSEI) and secondary electron imagery are used to analyse diatom assemblages from laminations and to determine interlamina relationships. Diatom observations are quantified with conventional assemblage counts. Laminae are primarily classified according to visually dominant species identified in BSEI and, secondarily, by terrigenous content. Nine lamina types are identified and are characterized by: Hyalochaete Chaetoceros spp. resting spores (CRS); CRS and Fragilariopsis spp.; Fragilariopsis spp.; Corethron pennatum and Rhizosolenia spp.; C. pennatum; Rhizosolenia spp.; mixed diatom assemblage; Stellarima microtrias resting spores (RS), Porosira glacialis RS and Coscinodiscus bouvet; and P. glacialis RS. Formation of each lamina type is controlled by seasonal changes in sea ice cover, nutrient levels and water column stability. Quantitative diatom assemblage analysis revealed that each lamina type is dominated by CRS and Fragilariopsis sea ice taxa, indicating that sea ice cover was extensive and persistent in the late Holocene. However the lamina types indicate that the sea ice regime was not consistent throughout this period, notably that a relatively warmer period, ~3100 to 2500 cal. yr BP, was followed by cooling which resulted in an increase in year round sea ice by ~1100 cal. yr BP.

Diatom abundance and paleo-temperature reconstruction for sediment cores from the southeast Norwegian Sea

Although the pulsating nature and the abruptness of the last deglaciation are well documented in marine and land records, very few marine records have so far been able to capture the high-frequency climatic changes recorded in the Greenland ice core Dye 3. We studied high-resolution sediment cores from SE Norwegian Sea, which display a detailed climatic record during the last deglaciation comparable to that of Dye 3. Accelerator mass spectrometry age control of the cores enables us to correlate this record in detail with continental records. The results indicate that the surface waters of the SE Norwegian Sea were seasonally ice free after 13,400 B.P. The Bølling/Allerød interstadial complex (13,200-11,200 B.P.) was a climatically unstable period with changing Arctic-Subarctic conditions. This period was punctuated by four progressively more severe sea surface temperature (SST) minima: between 12,900-12,800 B.P. (BCP I); 12,500-12,400 B.P. (BCP II); 12,300-12,000 B.P. (OD I); and 11,800-11,500 B.P. (OD II). The Younger Dryas (YD) (11,200-10,200 B.P.) represents the severest and most prolonged cold episode of this series of climatic deteriorations. It was bounded by very rapid SST changes and characterized by Arctic-Polar conditions. The first true warm Atlantic water incursion to the SE Norwegian Sea took place around 10,100 B.P., followed by a brief cooler condition between 9900-9600 B.P. (YD II). The early Holocene climatic optimum occurred between 8000-5000 B.P. A conceptual model is proposed where meltwater fluxes are suggested to cause the observed instability in the SST record.

The nitrogen costs of photosynthesis in a diatom under current and future pCO2

With each cellular generation, oxygenic photoautotrophs must accumulate abundant protein complexes that mediate light capture, photosynthetic electron transport and carbon fixation. In addition to this net synthesis, oxygenic photoautotrophs must counter the light-dependent photoinactivation of Photosystem II (PSII), using metabolically expensive proteolysis, disassembly, resynthesis and re-assembly of protein subunits. We used growth rates, elemental analyses and protein quantitations to estimate the nitrogen (N) metabolism costs to both accumulate the photosynthetic system and to maintain PSII function in the diatom Thalassiosira pseudonana, growing at two pCO2 levels across a range of light levels. The photosynthetic system contains c. 15-25% of total cellular N. Under low growth light, N (re)cycling through PSII repair is only c. 1% of the cellular N assimilation rate. As growth light increases to inhibitory levels, N metabolite cycling through PSII repair increases to c. 14% of the cellular N assimilation rate. Cells growing under the assumed future 750 ppmv pCO2 show higher growth rates under optimal light, coinciding with a lowered N metabolic cost to maintain photosynthesis, but then suffer greater photoinhibition of growth under excess light, coincident with rising costs to maintain photosynthesis. We predict this quantitative trait response to light will vary across taxa.