The Chicxulub impact caused a crash in productivity in the world's oceans which contributed to the extinction of ∼75% of marine species. In the immediate aftermath of the extinction, export ...productivity was locally highly variable, with some sites, including the Chicxulub crater, recording elevated export production. The long‐term transition back to more stable export productivity regimes has been poorly documented. Here, we present elemental abundances, foraminifer and calcareous nannoplankton assemblage counts, total organic carbon, and bulk carbonate carbon isotope data from the Chicxulub crater to reconstruct changes in export productivity during the first 3 Myr of the Paleocene. We show that export production was elevated for the first 320 kyr of the Paleocene, declined from 320 kyr to 1.2 Myr, and then remained low thereafter. A key interval in this long decline occurred 900 kyr to 1.2 Myr post impact, as calcareous nannoplankton assemblages began to diversify. This interval is associated with fluctuations in water column stratification and terrigenous flux, but these variables are uncorrelated to export productivity. Instead, we postulate that the turnover in the phytoplankton community from a post‐extinction assemblage dominated by picoplankton (which promoted nutrient recycling in the euphotic zone) to a Paleocene pelagic community dominated by relatively larger primary producers like calcareous nannoplankton (which more efficiently removed nutrients from surface waters, leading to oligotrophy) is responsible for the decline in export production in the southern Gulf of Mexico.
Plain Language Summary
The end Cretaceous mass extinction was caused by the impact of an asteroid in what is now the Yucatán Peninsula, México. The impact ejected aerosols and dust into the air that reduced sunlight transmission, causing a severe decline in photosynthesis and the collapse of marine food webs. However, the change in the amount of organic matter created by photosynthesizing plankton that was delivered to the seafloor (export productivity) was variable across the oceans. At some places, including the Chicxulub crater, export productivity was actually high immediately after the impact. We produced a ∼3‐million ‐year record of export productivity in the crater to determine how long it remained elevated and why it eventually declined. Export production was very high for the first 320,000 years after the impact, declined from 320,000 to 1,200,000 years after the impact, and then remained low. We found that this production was not related to the input of nutrients nor the degree of stratification of the ocean, but instead was probably driven by the increase in the cell size of phytoplankton. Larger phytoplankton removed nutrients from the surface waters as they sank, prompting an increase in species which are better adapted to low‐nutrient waters.
Key Points
Export productivity at Chicxulub was elevated for 1.2 Myr post K‐Pg; it was very high for the first 0.32 Myr and declined from 0.32–1.2 Myr
The final decline in export productivity ∼0.9–1.2 Myr is associated with the termination of calcareous nannoplankton disaster assemblages
Export productivity change is not correlated with stratification or terrigenous input and was likely driven by changes in the phytoplankton
We present LZIFU (LaZy-IFU), an IDL toolkit for fitting multiple emission lines simultaneously in integral field spectroscopy (IFS) data. LZIFU is useful for the investigation of the dynamical, ...physical and chemical properties of gas in galaxies. LZIFU has already been applied to many world-class IFS instruments and large IFS surveys, including the Wide Field Spectrograph, the new Multi Unit Spectroscopic Explorer (MUSE), the Calar Alto Legacy Integral Field Area (CALIFA) survey, the Sydney-Australian-astronomical-observatory Multi-object Integral-field spectrograph (SAMI) Galaxy Survey. Here we describe in detail the structure of the toolkit, and how the line fluxes and flux uncertainties are determined, including the possibility of having multiple distinct kinematic components. We quantify the performance of LZIFU, demonstrating its accuracy and robustness. We also show examples of applying LZIFU to CALIFA and SAMI data to construct emission line and kinematic maps, and investigate complex, skewed line profiles presented in IFS data. The code is made available to the astronomy community through github. LZIFU will be further developed over time to other IFS instruments, and to provide even more accurate line and uncertainty estimates.
We present the ~800 star formation rate maps for the SAMI Galaxy Survey based on H{\alpha} emission maps, corrected for dust attenuation via the Balmer decrement, that are included in the SAMI Public ...Data Release 1. We mask out spaxels contaminated by non-stellar emission using the O III/H{\beta}, N II/H{\alpha}, S II/H{\alpha}, and O I/H{\alpha} line ratios. Using these maps, we examine the global and resolved star-forming main sequences of SAMI galaxies as a function of morphology, environmental density, and stellar mass. Galaxies further below the star-forming main sequence are more likely to have flatter star formation profiles. Early-type galaxies split into two populations with similar stellar masses and central stellar mass surface densities. The main sequence population has centrally-concentrated star formation similar to late-type galaxies, while galaxies >3{\sigma} below the main sequence show significantly reduced star formation most strikingly in the nuclear regions. The split populations support a two-step quenching mechanism, wherein halo mass first cuts off the gas supply and remaining gas continues to form stars until the local stellar mass surface density can stabilize the reduced remaining fuel against further star formation. Across all morphologies, galaxies in denser environments show a decreased specific star formation rate from the outside in, supporting an environmental cause for quenching, such as ram-pressure stripping or galaxy interactions.
We present the first major release of data from the SAMI Galaxy Survey. This data release focuses on the emission-line physics of galaxies. Data Release One includes data for 772 galaxies, about 20% ...of the full survey. Galaxies included have the redshift range 0.004 < z < 0.092, a large mass range (7.6 < log(Mstellar/M\(_\odot\)) < 11.6), and star-formation rates of 10^-4 to 10^1\ M\(_\odot\)/yr. For each galaxy, we include two spectral cubes and a set of spatially resolved 2D maps: single- and multi-component emission-line fits (with dust extinction corrections for strong lines), local dust extinction and star-formation rate. Calibration of the fibre throughputs, fluxes and differential-atmospheric-refraction has been improved over the Early Data Release. The data have average spatial resolution of 2.16 arcsec (FWHM) over the 15~arcsec diameter field of view and spectral (kinematic) resolution R=4263 (sigma=30km/s) around Halpha. The relative flux calibration is better than 5\% and absolute flux calibration better than \(\pm0.22\)~mag, with the latter estimate limited by galaxy photometry. The data are presented online through the Australian Astronomical Observatory's Data Central.
In a motivating ward environment for schizophrenics, three methods of maximizing food as an effective reinforcer were tested. On the basis of pre-treatment measures, patients were classified as (1) ...“non-chronic meal missers” who served as control patients (Group A), (2) “chronic meal missers” because they had no tokens (Group B), or (3) “chronic meal missers” because they chose not to eat but had tokens (Group C). One of the following three experimental treatments was then administered when a patient missed a meal : (1) visual food priming (observing others eat), (2) oral food priming (sampling one teaspoon of each type of food for that meal), and (3) free meal (being offered a free meal when it was missed). Oral and visual food priming were found to be equally effective in increasing the percentage of meals bought by patients. A post-treatment follow-up for Group B found that this increase was even greater during the follow-up phase. The percentage of meals bought by patients in the free meal condition of Group B decreased during the treatment phase but was significantly above pre-treatment measures during the follow-up phase, suggesting that complete reinforcer sampling may also be an effective technique for increasing the percentage of meals bought.
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