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SDAG Monthly Meeting
Wednesday - April 17

Location: Sunbelt Publications
664 Marsat Ct # A
Chula Vista, CA

I-5 to Chula Vista to Palomar St. Exit east, right on Industrial Blvd., left on Anita St., left on Jayken Way, left on Marsat Ct. Suite A.
OR I-805: Chula Vista Orange Avenue exit, drive west to Third Avenue and turn left, drive south 2 blocks to Anita Street, turn right. Drive west past Broadway to Jayken Way and turn right. Drive north 1 block and turn right on Marsat Court, go to 664-A on the right. Park on the street, or in the parking lot in the back.

The Sunbelt location is open-ended to the outside, plan to bring a jacket or sweater in case it gets a little cold after the sun goes down.

happy hour
6:00pm -
Social hour  

SDAG Monthly Meeting

6:00pm - Happy Hour
7:00pm - Dinner
8:00pm - Program


Menu: Tacos (chicken, beef, pork), Rice & Beans with Guacamole & Chips (and Walawender Bar!)
if pre-registered by the deadline, $5 extra if you did not make a reservation. Click the SDAG member checkbox on the reservation form if you are a member.

Cost: $50.00 for non-members, $45.00 for members, $25.00 for students
Reservations: Make/Pay your reservation online by clicking the button below no later than noon, Tuesday, April 16
(Please note beginning January 2024 all meeting reservations will require on-line pre-payment due to venue costs, venue contracts, and loss of money due to no shows.)


8:00pm - Program

" Student research presentations by student scholarship winners, at Sunbelt Publications "

Speaker: Henry Arbaugh

Talk Title: The dynamics of microplastics in reef environments
Abstract: Microplastics (MPs) have been shown to stress tropical corals, making it important to understand the dynamics of MPs in reef environments. Unfortunately, most MP sediment studies can only report MP data from benthic sea-floor samples in units of concentration (#MPs/ml or #MPs/g sediment). Common collection methods (grabs, surface collection) cannot provide accurate measurements of MP accumulation rates because they do not include a depositional timeframe for the sediment. In contrast, collecting samples using sediment traps allows MP accumulation rates (#MP/area/day) to be calculated due to the known deployment length of the trap. Between 2009-16, sediment samples were collected monthly in sediment traps to monitor land-based pollution in near-shore and reef sites on St. John US Virgin Islands, a high island surrounded by sensitive coral reef habitats affected by land-based pollution. For this study, frozen archived sediment trap samples were utilized. To extract the MPs from the sediment, we employed a 3- step phased centrifugation density separation method including (1): interstitial water removal, (2): hydrogen peroxide treatment to remove organic matter, and (3): a zinc chloride solution density separation. MP identification was conducted via bright field microscopy, and confirmation of suspected MP particles was performed using the 'hot needle test'. A total of 1672 particles were identified across seven shore samples and nine reef samples. Sample volumes had a range of 12.5-40mL, which resulted in a concentration range of 153-6622 MPs/100mL sediment. Accumulation rate values had a range of 0.018-0.484 MPs/day/cm2. Notably, our experiments showed that a potentially high percentage of MPs found in the samples were located in the interstitial water phase (16±12%) and the following hydrogen peroxide phase (25±20%), which is significant because literature review shows that many studies often discard intermediate treatment solutions, which may result in an underestimation of total MP values. Additionally, MP concentrations in the sediment trap samples were found to be much greater than those observed in benthic samples from other comparable locations, which may be due to differing analytical methodology, time frames of deposition, post depositional processes, and/or hydrologic/resuspension processes that affect accumulation in the sediment traps.

Speaker: Bradley Keith

Talk Title: Patagonia ice sheet and Southern Westerly Wind driven variations in Chilean Margin sediment over the past 900,000 years
Abstract: Paleoceanographic archives from the Chilean Margin have disproportionately impacted our understanding of southern hemisphere climate due to their exceptional time resolution and proximity to the Antarctic Circumpolar Current (ACC) and the Southern Westerly Winds (SWW). Here we present new data from Chilean Margin Site J1001, recovered during Expedition 379T (a.k.a. JR100) from the abyssal plane approximately 130 km west of Southern Chile at (46.4053S, 77.3242W, 3067 m water depth). Shipboard paleomagnetic and biostratigraphic data place the base of the core at ~900 ka. Low resolution benthic d18O data and correlation of the aluminum content of the sediments to ice core records of Antarctic temperature confirm and refine the shipboard chronology. We measured downcore variations in the bulk sediment geochemistry of Site J1001 every 1 cm via XRF core scanning. Variations in the abundances of the terrestrial elements (Al, Si, K, Fe, Ti, Zr, and Rb) reflect changes in the flux, provenance, and grain size of sediments delivered to the Chilean Margin and post-depositional processes. We observe significant glacial-interglacial variability in the bulk geochemistry at Site J1001, with higher ratios of zirconium to rubidium (Zr/Rb) and lower ratios of titanium to potassium (Ti/K) during interglacial periods. We speculate that the observed variations can be linked to changes in sedimentary sources controlled by the extent of the Patagonia Ice Sheet. Significant power is also seen at 11.5 ky, corresponding to a half precession cycle in Zr/Rb and Ti/K and an in-phase relationship at this timescale between the two ratios, indicating control by grain-size. We hypothesize the half precession signal is linked to the latitudinal migration of the SWW, via their control on regional precipitation and erosion and/or the position and strength of the ACC and bottom water flow speeds at the core site. Although a half-precession signature has not been observed in records of the SWW previously, prior work at the northern margin of the SWW range along the Chilean Margin indicates strong precession (23/19 ka) cycles in their position over the last 1 million years (Lamy et al., 2019). We suggest the half-precession signature at Site J1001 reflects the cores location near the mid-point of SWW latitudinal range.

Speaker: Sarah Engel

Talk Title: No title at the time of newsletter publication
Upcoming SDAG meetings - 2024

May 15- Don Barrie & William Buckley present some Icelandic Adventures

Monday June 17- SDAG / SCGS joint meeting: Susan Hough on 1994 Northridge Earthquake - Meeting at El Adobe in San Juan Capistrano.

July 17- Chuck Houser, at Sunbelt Publications

August 21- Dr. Pat Abbott presents Strata, Paleoclimates, & Asteroid Impact Interpretations.

September 27 - 29- SDAG Annual Field Trip, to the Transverse Ranges (no meeting this month)

October 16- Mike Ziegler on gravitation. Meeting at Sunbelt Publications.

First Wednesday November 6- Joint Meeting with AEG Inland Empire Section/ Jahn's Lecturer Cynthia Palomares in Fallbrook.

December 18- Traditional Holiday Celebration at the NAT with Tom Demere

Recordings of past meetings

3/19/2024 Mighty Bad Land: A Perilous Expedition to Antarctica Reveals Clues to an Eighth Continent - Bruce Luyendyk

Meetings are usually scheduled for the 3rd Wednesday evening of the month. Meeting information on this website is normally updated the second week of the month.

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