Coastal upwelling is a common oceanographic phenomenon around the world. It typically involves the upsurge of cold, nutrient-rich waters from depths while surface waters move offshore. The increased nutrient concentration in the euphotic zone of coastal waters fuels pelagic primary productivity, ultimately benefiting coastal fisheries through bottom-up effects (Du et al., 2024). In addition, the cooling of coastal waters moderates coastal weather through air–water heat fluxes (Clancy et al., 1979; Dabuleviciene et al., 2024) and can affect the thermal physiology of coastal organisms (Thiel et al., 2007). Coastal upwelling can also affect the larval supply of intertidal invertebrates, influencing their recruitment and indirectly food web structure (Menge et al., 2019). For these reasons, understanding the drivers of the intensity of coastal upwelling has traditionally been an important goal in marine science.

Coastal upwelling is often caused by winds. Persistent alongshore winds blowing with the coast on the left in the northern hemisphere or on the right in the southern hemisphere trigger (due to stress and Coriolis forcing) an offshore transport of surface waters that are ultimately replaced by upwelled waters (Stewart, 2008). One of the largest systems of that kind in the world is the Peruvian coastal upwelling system, in the eastern South Pacific (Tarazona and Arntz, 2001). Upwelling can be particularly strong on that coast driven by equatorward alongshore winds (Chamorro et al., 2018) and has been linked to a high pelagic productivity (Bakun and Weeks, 2008; Espinoza et al., 2017; Massing et al., 2022). A major factor affecting the intensity of upwelling on that coast is the El Niño–Southern Oscillation (ENSO). ENSO is a seasonal-scale climatic pattern determined by differences in atmospheric pressure between the western and eastern tropical Pacific. While most years exhibit typical upwelling conditions on the Peruvian coast, the two extreme phases of ENSO (called El Niño and La Niña) alter those conditions. In the El Niño phase, the equatorial trade winds weaken and warm surface waters move from the central Pacific to the Peruvian coast, deepening the coastal thermocline (Chamorro et al., 2018). The intensity of upwelling on that coast during El Niño depends on the balance between local alongshore winds (which typically intensify with El Niño) and a compensating onshore current, but overall the upwelling of cold waters decreases because the thermocline remains deeper with El Niño (Espinoza-Morriberón et al., 2017). In the La Niña phase, the reverse is true, as the upwelling of cold waters intensifies above normal levels on that coast (Espinoza-Morriberón et al., 2017).

Although ENSO is eminently a Pacific phenomenon, it also affects other parts of the world through climatic teleconnections. In fact, ENSO is considered to be a major driver of global interannual climate variability (Timmermann et al., 2018). Thus, ENSO-related changes in atmospheric pressure and winds have been recorded around the globe (Kim et al., 2023; Alizadeh, 2024; Beverley et al., 2024; Park and Son, 2024; Cai et al., 2025; Miao et al., 2025). As a consequence, ENSO is also related to variability in wind-driven upwelling on other coasts in the Pacific Ocean (Thiel et al., 2007; Jacox et al., 2015; Li et al., 2025) as well as on coasts in the Indian Ocean (Vinayachandran et al., 2021; Nigam and Pant, 2024; Rachman et al., 2024) and Atlantic Ocean (Roy and Reason, 2001; Rouault and Tomety, 2022).

The Atlantic coast of Canada in Nova Scotia exhibits areas of wind-driven upwelling, but links between ENSO and upwelling intensity on that coast are poorly understood. This is likely because coastal upwelling on this western ocean boundary is less prominent relative to other shores, particularly those exhibiting strong upwelling on eastern ocean boundaries (Kämpf and Chapman, 2016). Off the southwestern coast of Nova Scotia, which faces the outer Gulf of Maine (Figure 1), upwelling is mainly caused by tidal mixing and submarine topography (Tee et al., 1993; Chegini et al., 2018). However, on the southeastern coast of Nova Scotia, which faces the open Atlantic Ocean (Figure 1), upwelling is mainly caused by winds (Petrie et al., 1987; Shan et al., 2016; Shan and Sheng, 2022), particularly in July triggered by southwesterly winds blowing parallel to the shore (Petrie et al., 1987). On this coast, upwelling in July was found to be weaker under El Niño conditions than under ENSO-neutral conditions (Scrosati and Ellrich, 2020). However, only two years were contrasted in that study, revealing the need to analyze more years to better evaluate to what extent upwelling may be related to ENSO on this coast. This Data Report provides data on July upwelling and ENSO for the last 39 years (1987 to 2025) to investigate the generality of this relationship for this coast. In addition, this article provides data on coastal surface seawater temperature (SST) to show that, ultimately, increases in July upwelling on this coast are related to coastal ocean cooling. These data are hereby made publicly available to facilitate future studies on upwelling–ENSO dynamics in this part of the world.

We quantified coastal upwelling using Bakun’s upwelling index (BUI), which is based on wind data and geographic information (Bakun, 1973). The wind data were retrieved from records (Government of Canada, 2025) generated by a land weather station called Western Head (N 43.9900, W 64.6642; Figure 1), which is situated less than 300 m from the coast in a region with flat terrain. The Western Head area is representative of the thermal conditions (Scrosati et al., 2020) and intertidal biological communities (Scrosati et al., 2022) that characterize the southeastern coast of Nova Scotia. Other land weather stations in this region are farther away from the coast, making their wind data less reliable to calculate wind-driven coastal upwelling. The earliest year for which we retrieved wind data was 1987 because, before that year, there were often gaps in the data in terms of hours, days, or even weeks, while from 1987 onwards wind data were recorded hourly mostly every day. For the month of July of each studied year (1987 to 2025), we calculated an average value of BUI for Western Head following the steps detailed in a recent article (Scrosati et al., 2025). Essentially, those calculations used equation 4.2 in Stewart (2008) to calculate wind stress, equation 2.2 in Kämpf and Chapman (2016) to calculate Ekman transport, and finally equation 2.3 in Kämpf and Chapman (2016) to calculate BUI. To describe the ENSO conditions in July from 1987 to 2025, we retrieved from NOAA (2025) the corresponding values of the Oceanic Niño Index (ONI) centered in July. For any given month, ONI is published as the rolling 3-month average temperature anomaly in the surface waters of the east-central tropical Pacific (NOAA, 2025). To characterize SST for our coast, we used data measured remotely by satellites (NASA, 2025) between 2002 and 2025 (no data were available before 2002). For the month of July of each of those years, we retrieved all available daily SST data for the 4-km-x-4-km cell that includes Western Head (N 43.9896, W 64.6607), which is a major rocky headland (Figure 1) often used for intertidal ecology (Scrosati and Holt, 2021; Cameron and Scrosati, 2023; Scrosati and Cameron, 2023; Scrosati and Ellrich, 2025) located near the weather station of the same name. When SST data for that cell size were unavailable for certain days, we filled the gaps using data for the 9-km-x-9-km cell that includes Western Head whenever available. With those values, we calculated mean July SST for each year from 2002 to 2025. In the next section, we discuss the main patterns revealed by the data. The dataset used for this article is freely available from the Zenodo online repository (Ellrich and Scrosati, 2026).

Between 1987 and 2025, BUI was always positive for the month of July at Western Head, indicating a consistent predominance of upwelling (not downwelling) conditions (Figure 2). Interannual variability was clear, as the highest value of July BUI (recorded in 2014) was 6 times higher than the lowest value (recorded in 1997; Figure 2). During these 39 years, ENSO conditions in July spanned the full range from El Niño (ONI > 0.5) to La Niña (ONI < -0.5) conditions, with many years having ENSO-neutral conditions (ONI between -0.5 and 0.5; Figure 2). For these 39 years, BUI in July was negatively related to ONI (r = -0.427, P = 0.007; Figure 2), ONI explaining a moderate amount of variation in BUI (18.2%). For the 24 years between 2002 and 2025, SST in July was negatively related to BUI (r = -0.425, P = 0.039; Figure 2), with a 18.1% of the variation in SST being explained by BUI.

The main contribution of this multiannual dataset is the confirmation of an inverse relationship between the intensity of wind-driven upwelling on the southeastern Nova Scotia coast and ONI as a measure of ENSO conditions. On average, coastal upwelling weakened under El Niño conditions (ONI > 0.5) and strengthened under La Niña conditions (ONI < -0.5) relative to the intermediate values expected under ENSO-neutral conditions. Therefore, this pattern for Nova Scotia agrees with links between ENSO and wind-driven upwelling noted for other coasts of the world far away from the Peruvian upwelling system (see references above). This pattern also strengthens the notion of distant teleconnections between ENSO and conditions outside of the Pacific basin. The specific mechanisms underlying the link found for Nova Scotia between coastal upwelling and ENSO could be investigated through climatic and oceanographic modelling, as done for equivalent cases elsewhere in the world (see above references). In a way, the pattern revealed by this dataset for Nova Scotia resembles the so-called “coastal El Niño” phenomenon seen occasionally on the Peruvian coast. The “coastal” El Niño (name used to differentiate it from the basin-scale El Niño described in the Introduction) also warms coastal Peruvian waters but through a direct decrease of coastal upwelling (Peng et al., 2024). In Nova Scotia, weaker coastal upwelling was indeed related to warmer surface waters (Figure 2).

Another contribution of this dataset is the confirmation of the relatively moderate intensity of upwelling on the southeastern Nova Scotia coast. Between 1987 and 2025, the highest daily value of BUI in July (when upwelling is important; Petrie et al., 1987) was 161 m³ s^-1 (100 m of coastline)^-1 (in 2014), but the highest daily value for the other 38 years ranged only between 20 and 97 m³ s^-1 (100 m of coastline)^-1 (see all daily values in Ellrich and Scrosati, 2026). Moreover, for these 39 years, the monthly averages for July ranged between 5 and 30 m³ s^-1 (100 m of coastline)^-1 (Figure 2). These values contrast with those that characterize the major systems of coastal upwelling in the world, which occur on eastern ocean boundaries where BUI can reach or surpass 500 m³ s^-1 (100 m of coastline)^-1 (Schwing et al., 1996; Demarcq, 1998; Menge and Menge, 2013; Costa Goela et al., 2016; Kämpf and Chapman, 2016).

Ultimately, through its influences on the intensity of coastal upwelling, ENSO affects the growth, reproduction, and survival of coastal pelagic (Galán and Baylón, 2025; Galloso et al., 2025) and benthic (Bosman et al., 1987; Ladah et al., 1999; Scrosati, 2001; Lourenço et al., 2020; Scrosati and Ellrich, 2025; Nava et al., 2025) organisms and communities. Therefore, it is reasonable to speculate that the interannual variation observed in species abundance on the Nova Scotia coast (Scrosati et al., 2022, 2025) might at least partially respond to this climatic–oceanographic coupling. Overall, understanding these links continues to be a highly relevant component of coastal marine science.