Since 1988, the Hawaii Ocean Time-series (HOT) program has provided information on time variability in biogeochemical and physical processes in one of Earth's largest ecosystems, the North Pacific Subtropical Gyre (NPSG).  The program is built around interdisciplinary shipboard sampling and data collection at near monthly intervals (~10 cruises/year) at the open ocean site Station ALOHA (22.75 degrees N, 158 degrees W).  Observations, measurements, and the results of experiments conducted at Station ALOHA continue to shape our understanding of linkages between ocean biogeochemistry, plankton ecology, and the physical forces that influence the ocean’s ecological functioning. One salient outcome of the ~35 year record at HOT is a clear demonstration that the ocean varies over a range of time scales, with anthropogenic forcing contributing an added layer of complexity. In the growing effort to distinguish between natural and human-induced variability, sustained ocean time-series such as HOT are of critical importance as they represent one of the few long-term, temporally resolved observing assets scientists have to characterize and quantify marine ecosystem response to a highly dynamic and changing climate system. Two exemplar outcomes of this effort include characterization of the seasonality and trends in ocean productivity and ocean acidification. Specifically, HOT data has revealed an unexpected increase in rates of primary production, the metabolic process that fuels and supports ocean food chains. Layered over seasonal, interannual, and quasi-decadal variability in rates of production, is a significant linear increase in the 0-200 m depth-integrated rate of primary productivity, with a large relative increase in the lower portion (75 -125 m) of the sunlit zone of the water column (Figure 1). We hypothesize this trend to be a consequence of anthropogenic nutrient additions to the open ocean. Changes in the chemical composition of seawater are also emerging. In response to rising carbon dioxide in the atmosphere, the HOT program has documented progressive decreases in seawater pH (Figure 2) with apparent acceleration of acidification in the mesopelagic (~500 m). These documented patterns in ocean biology and chemistry illustrate how HOT has served to provide reference baselines for essential ocean variables. These data help to characterize natural patterns of ocean system variability and associated links to regional climate indices, as well as support calibration/validation of autonomous in situ and remote (satellite, airborne) sensors (Figure 1). The measurements collected through the HOT program are augmented by continuous measurements at the surface by the Woods Hole - HOT (WHOTS) mooring, a designated "Ocean Reference Station," and the ALOHA Cabled Observatory (ACO). Together, HOT, WHOTS and ACO provide complete water-column measurements at high precision and temporal resolution. These data are an invaluable baseline for understanding process and change in the vast NPSG.

In lockstep with the scientific mission to observe this region of the North Pacific is the mission to share our data in an open and timely manner and to provide access to the sea for broader community as well as a sense of ecological context that allows other scientists to frame their observations and hypotheses. All HOT data are publicly available, quality controlled, and transmitted to BCO-DMO (https://www.bco-dmo.org/project/2101). We have also worked with an Earth-cube RCN for Marine Ecological Time Series (METS) to bring together different cross-sections of the marine ecological time-series community (i.e. data producers, users, scientists, and managers) in large- and small-group formats to foster the necessary dialog to develop FAIR (Findable, Accessible, Interoperable, Reproducible) data solutions and practices. 

HOT has routinely provided access to the sea for students, educators, scientists, science journalists as well as volunteers fascinated with the ocean that want to understand how ocean monitoring programs operate. Since 1988, >250 researchers from >80 institutions have participated in HOT cruises. Numerous M.S. and Ph.D. degrees (55 to date that we know of) have been awarded based on HOT related research projects and HOT data have been incorporated into classrooms at all learning levels. Students and post-docs routinely rely on HOT for their research: the short duration cruises do not require extended absences from the classroom, and the rich historical dataset is ideal for developing testable hypotheses. Beyond basic knowledge generation, a critical outcome of this project is dissemination of the knowledge gained. Over >800 peer-reviewed journal articles and invited book chapters that have resulted from HOT program observations, data synthesis, and modeling have been published. Collectively, this body of work represents a unique and diverse knowledge base on the NPSG.

Last Modified: 10/29/2024
Modified by: Angelicque E White