In Situ Observations of Pelagic Sargassum Total and Morphotype-specific Density and Distribution Across the Western North Atlantic from 1993 to 2023.

Between 1993 and 2023, 5,587 neuston net tows were conducted onboard Sea Education Association’s (www.sea.edu) SSVs Westward and Corwith Cramer during oceanographic research cruises across the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Cruise tracks varied seasonally and annually. The neuston net (1.0m × 0.5m frame, 33​3​ um mesh) was deployed from a boom extended 5 m off the ship’s port side while sailing on a port tack. Any wind​r​ows of Sargassum were thus crossed perpendicularly and any bow wake effect was minimized. Tows were conducted at two knots for 30 minutes for a typical distance of ~1.0 nm; tow distance (m) was calculated as the difference between start/end GPS locations (1993–2003) and from minute-by-minute GPS locations (2004–2023). Standard net processing included identifying pelagic Sargassum specimens to morphotype, patting dry, and weighing using a spring scale to yield mass (g) for each morphotype. Three common holopelagic morphotypes are reported: Sargassum natans var. natans (Sn_n), S. natans var. wingei (Sn_w), and S. fluitans (Sf). Weighted arithmetic mean Sargassum density (g/km2) was calculated from the sum of Sargassum mass divided by the sum of tow area for all tows in a given year (season, time frame) for a given region. Morphotypes reported as percentage of total collected biomass in a given year (season, time frame) for a given region. The date and GPS position were captured with each sample. All net tows were assigned to one of five regions defined on the basis of physical oceanographic boundaries. Analysis of data was organized by ecological year (March–February, corresponding with the start of the annual spring bloom period in the Sargasso Sea) and season (spring/summer March-August, fall/winter September-February). In most years, neuston tows occurred during both the spring/summer and fall/winter seasons in a region; sporadic changes in cruise track may have caused occasional missed seasons. Examined time frames (pre-MODIS 1993-1999, pre-GASB 2000-2010, early GASB 2011-2014, and recent GASB 2015-2023) were selected for comparison with satellite data and Great Atlantic Sargassum Belt (GASB) dynamics. Quality control confirmed accurate, consistent data entry and GPS positions, and filtered out incomplete records. Blank cell = no data.1993年至2023年间，海洋教育协会（Sea Education Association，官网：www.sea.edu）旗下的SSV Westward号与SSV Corwith Cramer号科考船，在覆盖北大西洋、加勒比海与墨西哥湾的海洋考察航次中，累计完成5587次表层浮游生物网（neuston net）拖网作业。各航次的航行轨迹随季节与年度动态调整。 本次使用的表层浮游生物网（框架尺寸1.0m × 0.5m，网目孔径333μm）通过船舶左舷伸出的5米吊杆布设，此时船舶处于左舷受风航态。该布设方式可确保拖网垂直穿过马尾藻（Sargassum）风聚带，同时最大程度降低船首尾流对采样的干扰。常规拖网作业以2节航速持续30分钟，典型拖行距离约1.0海里；拖网距离（米）的计算方式为：1993年至2003年采用起始与终止GPS位置的差值，2004年至2023年则采用逐分钟记录的GPS位置计算得到。 标准网样处理流程包括：将远洋性马尾藻标本按形态型分类、吸干表面水分，随后使用弹簧秤称重，以获取各形态型的生物量（克）。本次数据集公开了3种常见的全远洋性马尾藻形态型：漂浮马尾藻原变种（Sargassum natans var. natans，缩写Sn_n）、漂浮马尾藻温氏变种（S. natans var. wingei，缩写Sn_w）以及浮水马尾藻（S. fluitans，缩写Sf）。 加权算术平均马尾藻种群密度（克/平方千米）的计算方式为：针对给定区域、给定年度（季节、时间区间）内的所有拖网作业，以总马尾藻生物量之和除以总扫海面积之和得到。各马尾藻形态型的占比以给定区域、给定年度（季节、时间区间）内的总采集生物量百分比形式统计呈现。 每份样本均同步记录采样日期与GPS位置信息。所有拖网作业均被划分至基于物理海洋学边界划定的5个研究区域中。数据整理按生态年度（3月至次年2月，对应马尾藻海年度春季水华的起始时段）与季节（春夏季：3-8月；秋冬季：9-2月）进行。 多数年份中，各研究区域的表层浮游生物拖网作业会覆盖春夏季与秋冬季两个采样时段；航迹的偶发变动可能导致个别时段的采样缺失。本次数据集选取了以下时间区间以匹配卫星观测数据与大西洋马尾藻带（Great Atlantic Sargassum Belt，缩写GASB）的动态变化：MODIS前置时段（1993-1999年）、GASB前置时段（2000-2010年）、GASB早期时段（2011-2014年）以及GASB近期时段（2015-2023年）。 质量控制环节确认了数据录入与GPS位置记录的准确性与一致性，并过滤了不完整的样本记录。空白单元格代表无有效数据。