Which region in New Zealand produces the largest quantity of Merlot?

Hawke's Bay is recognized as the region in New Zealand that produces the largest quantity of Merlot. This region benefits from a warmer climate, which is conducive to growing ripe and full-bodied red wines, including Merlot. The diverse terroir of Hawke's Bay, which includes a mix of river and coastal influences, allows for a range of styles and expressions of Merlot.

In contrast, while Marlborough is famous primarily for its Sauvignon Blanc, it doesn't have the same level of prominence for Merlot production. Waipara Valley, known for its cooler climate, tends to focus more on varieties such as Pinot Noir and Chardonnay. Central Otago, renowned for its exceptional Pinot Noir, also does not produce Merlot in significant quantities compared to Hawke's Bay. Therefore, Hawke's Bay stands out as the key region for Merlot in New Zealand, making it the correct answer.