Alana Sherman

Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean

Significance Global warming is now a well-documented phenomenon that is influencing every aspect of our world, from increased storm intensity to melting of polar ice sheets and rising sea level. The impact of such changes in climate is least known for the deep ocean, which covers over 60% of the earth’s surface. An unprecedented 24-y time series measuring changes in food supply and utilization by benthic communities at 4,000-m depth in the deep northeast Pacific reveal strong connectivity with changing surface ocean conditions, which have broad implications for the global carbon cycle. The deep ocean, covering a vast expanse of the globe, relies almost exclusively on a food supply originating from primary production in surface waters. With well-documented warming of oceanic surface waters and conflicting reports of increasing and decreasing primary production trends, questions persist about how such changes impact deep ocean communities. A 24-y time-series study of sinking particulate organic carbon (food) supply and its utilization by the benthic community was conducted in the abyssal northeast Pacific (∼4,000-m depth). Here we show that previous findings of food deficits are now punctuated by large episodic surpluses of particulate organic carbon reaching the sea floor, which meet utilization. Changing surface ocean conditions are translated to the deep ocean, where decadal peaks in supply, remineralization, and sequestration of organic carbon have broad implications for global carbon budget projections.

Icebergs as Unique Lagrangian Ecosystems in Polar Seas

Global warming and its disproportionate impact on polar regions have led to increased iceberg populations. Southern Ocean studies in the northwest Weddell Sea have verified substantial delivery of terrestrial material accompanied by increased primary production and faunal abundance associated with free-drifting icebergs. It is hypothesized that input and utilization of macro- and micronutrients are promoted by conditions unique to free-drifting icebergs, leading to increased production, grazing, and export of organic carbon. In Arctic regions, increased freshwater input from meltwater acts to stratify and stabilize the upper water column. As has been observed in the Southern Ocean, Arctic-region icebergs should drive turbulent upwelling and reduce stratification, potentially leading to increased nitrate delivery to the local ecosystem. Increasing populations of icebergs in polar regions can potentially be important in mediating the drawdown and sequestration of CO(2) and can thus impact the oceanic carbon cycle.

Development of an Active, Large Volume, Discrete Seawater Sampler for Autonomous Underwater Vehicles

Engineers and researchers at the Monterey Bay Aquarium Research Institute (MBARI) have developed a water sampler that rapidly captures a 2-liter sample of seawater. This syringe-like sampler is spring actuated and can acquire a full sample in less than two seconds. This sampler will complement the wide array of sensors currently integrated on MBARIs autonomous underwater vehicles (AUVs). Although many properties of seawater can be analyzed by AUV onboard sensors, these measurements alone are often insufficient to fully investigate important scientific questions. Returning a discrete sample of seawater from the field, via an AUV, for laboratory analysis will expand the spectrum of research possible with AUV platforms. Using AUV onboard intelligence, designated sites and important phenomena can be targeted for acquiring water samples. This paper addresses the development, testing, and initial deployments of this sampler.

From the surface to the seafloor: How giant larvaceans transport microplastics into the deep sea

Larvaceans can filter microplastics from the water and package them into their fecal pellets, transporting them into the deep sea. Plastic waste is a pervasive feature of marine environments, yet little is empirically known about the biological and physical processes that transport plastics through marine ecosystems. To address this need, we conducted in situ feeding studies of microplastic particles (10 to 600 μm in diameter) with the giant larvacean Bathochordaeus stygius. Larvaceans are abundant components of global zooplankton assemblages, regularly build mucus “houses” to filter particulate matter from the surrounding water, and later abandon these structures when clogged. By conducting in situ feeding experiments with remotely operated vehicles, we show that giant larvaceans are able to filter a range of microplastic particles from the water column, ingest, and then package microplastics into their fecal pellets. Microplastics also readily affix to their houses, which have been shown to sink quickly to the seafloor and deliver pulses of carbon to benthic ecosystems. Thus, giant larvaceans can contribute to the vertical flux of microplastics through the rapid sinking of fecal pellets and discarded houses. Larvaceans, and potentially other abundant pelagic filter feeders, may thus comprise a novel biological transport mechanism delivering microplastics from surface waters, through the water column, and to the seafloor. Our findings necessitate the development of tools and sampling methodologies to quantify concentrations and identify environmental microplastics throughout the water column.

New technology reveals the role of giant larvaceans in oceanic carbon cycling

Novel instrumentation reveals that mucus-filter-feeding deep-sea larvaceans play a large role in oceanic carbon cycling. To accurately assess the impacts of climate change on our planet, modeling of oceanic systems and understanding how atmospheric carbon is transported from surface waters to the deep benthos are required. The biological pump drives the transport of carbon through the ocean’s depths, and the rates at which carbon is removed and sequestered are often dependent on the grazing abilities of surface and midwater organisms. Some of the most effective and abundant midwater grazers are filter-feeding invertebrates. Although the impact of smaller, near-surface filter feeders is generally known, efforts to quantify the impact of deeper filter feeders, such as giant larvaceans, have been unsuccessful. Giant larvaceans occupy the upper 400 m of the water column, where they build complex mucus filtering structures that reach diameters greater than 1 m. Because of the fragility of these structures, direct measurements of filtration rates require in situ methods. Hence, we developed DeepPIV, an instrument deployed from a remotely operated vehicle that enables the direct measurement of in situ filtration rates. The rates measured for giant larvaceans exceed those of any other zooplankton filter feeder. Given these filtration rates and abundance data from a 22-year time series, the grazing impact of giant larvaceans far exceeds previous estimates, with the potential for processing their 200-m principal depth range in Monterey Bay in as little as 13 days. Technologies such as DeepPIV will enable more accurate assessments of the long-term removal of atmospheric carbon by deep-water biota.

MARS Benthic Rover: In-situ rapid proto-testing on the Monterey Accelerated Research System

The Benthic Rover is an autonomous, bottom-crawling vehicle being developed at the Monterey Bay Aquarium Research Institute (MBARI) to conduct long-term deep-ocean ecological research. In 2009 MBARI researchers deployed the Rover on the Monterey Accelerated Research System (MARS) cabled observatory for component and operational testing. MARS is located near-shore in the Monterey Bay near Monterey, CA, at a depth of approximately 900 meters, providing the power reliability and network accessibility similar to an on-shore laboratory. By enabling immediate feedback and the ability to quickly re-program control software and re-configure mission scripts, MARS facilitates a kind of “in-situ rapid proto-testing”. MBARI researchers were able to run numerous experimental procedures and analyze results in a relatively short timeframe, converging on desired operational profiles quickly and at very low cost. This paper will cover recent development work on the Benthic Rover with emphasis on the deployment and testing on MARS.

Initial Deployments of the Rover, an Autonomous Bottom-Transecting Instrument Platform for Long-Term Measurements in Deep Benthic Environments

Rover is a bottom-crawling, autonomous vehicle capable of making continuous time-series measurements at abyssal depths up to 6000 m for periods exceeding six months. The Rover control system and instrumentation suite are being designed at the Monterey Bay Aquarium Research Institute (MBARI), building on the earlier rover work of Smith and associates at the Scripps Institution of Oceanography. The vehicle weighs 68 kg in water and crawls on two wide tracks with a combined surface contact area of about one square meter; this provides good traction while minimizing the disturbance to benthic sediments. A typical mission scenario is to take measurements for a few days at each site before picking up the instruments and moving forward ~10 m to a new site. Up to fifty sites may be visited in a single mission. Engineering field tests have been performed with the Rover in the Monterey Bay in California (890 m depth), and at Station M, 220 km west of the central California coast (4200 m depth). Rover operations have been observed with the ROVs Ventana and Tiburon, and with the manned submersible DSV Alvin. Knowledge gained from these engineering deployments has resulted in numerous modifications and improvements to The Rover.

Lessons Learned while Optimizing Instrument Sensitivity for Deep Ocean Raman Spectroscopy

Over the last several years, scientists and engineers at the Monterey Bay Aquarium Research Institute (MBARI) have successfully developed and deployed two generations of deep ocean laser Raman spectrometers. There are many advantages to this type of Spectroscopy: it is rapid, non-destructive, and can be used to analyze solids, liquids, and gases. Unfortunately, one of the disadvantages of using Raman Spectroscopy is that the return signal measured is very weak. Thus, it is difficult to detect dilute chemical compounds in solution, such as bicarbonate and carbonate ions at natural concentrations. This paper discusses the efforts we have made to increase the sensitivity of our second generation Deep Ocean Raman In Situ Spectrometer (DORISS2). In developing this second generation instrument, we incorporated new components which improved system performance. These components include a new ruggedized U-shaped spectrometer and a back-illuminated CCD camera which is much more sensitive than our original front-illuminated CCD camera. The element which has had the most impact on system sensitivity is a set of new custom-made fiber optic cables. We had built several sets of custom fiber optic cables, but despite our efforts, their performance degraded substantially over time. Recently, we developed a new oil-filled pressure-compensated fiber optic cable which performs far better in pressure testing and is much more robust. At 6000 psig, this cable shows losses of only 2-3 dB versus our previous cables where losses of 25-30 dB were common. This new fiber optic cable was field tested in May and showed markedly improved performance

Laser Raman spectroscopic instrumentation for in situ geochemical analyses in the deep ocean

Engineers and scientists at the Monterey Bay Aquarium Research Institute (MBARI) have successfully developed instrumentation for performing laser Raman spectroscopy in the deep ocean. Laser Raman spectroscopy is a form of vibrational spectroscopy that is capable of performing rapid, nondestructive, in situ geochemical analyses. The Deep Ocean Raman In Situ Spectrometer (DORISS) is based on a laboratory model laser Raman spectrometer from Kaiser optical systems, Inc. The sample is interrogated by a 532 nm laser and the Raman backscattered radiation passes through a holographic grating and is recorded on a CCD camera. Laser Raman spectroscopy is capable of analyzing a variety of solid, liquid and gaseous species. Due to the strict requirements for positioning the laser focal point when analyzing opaque samples, a Precision Underwater Positioning (PUP) system was built to position the DORISS probe head with respect to the sample. PUP is capable of translating the DORISS probe head in 0.1 mm increments with 1 mm repeatability. DORISS and PUP are deployed by MBARIs remotely operated vehicles - ROVs Tiburon and Ventana - and are controlled by a scientist aboard the surface ship. DORISS and PUP have been deployed a number of times in Monterey Bay, the Gulf of California, and Hydrate Ridge, Oregon for testing and analyses of natural targets of interest. The development of smaller, second generation systems will allow DORISS and PUP to be carried on other deep submergence vehicles for use by the wider oceanographic community.