Question: Black Brook is a tributary of the Merrimack River which flows to a gulf of what ocean?

Context paragraphs:
Pemigewasset Lake: Pemigewasset Lake is a 249 acre water body located in the Lakes Region of central New Hampshire in the United States.  The lake straddles the border between the towns of New Hampton and Meredith, both in Belknap County.  Outflow from the lake travels down Harper Brook to the Pemigewasset River, a tributary of the Merrimack River, which flows to the Gulf of Maine.

Black Brook (Passaic River): Black Brook is a tributary of the Passaic River that flows through the Great Swamp National Wildlife Refuge in Morris County, New Jersey in the United States.  Black Brook rises at the north east base of Long Hill, Chatham Township, Morris County, flows westerly along the hill, by a course of 7 or 8 miles to its recipient in Morris Township, New Jersey.  Due to the chemical fertilizer usage in nearby areas, Black Brook has the second worst water quality after Loantaka Brook.

Crystal Lake (Gilmanton, New Hampshire): Crystal Lake is a 455 acre water body located in Belknap County in the Lakes Region of central New Hampshire, United States, in the town of Gilmanton.  Crystal Lake is at the head of the Suncook River watershed.  Water flows into Crystal Lake from the Belknap Range through Manning and Sunset lakes to the north.  Water from Manning Lake enters Crystal Lake via Nelson Brook.  Other waterways flowing into Crystal Lake include Wasson Brook and Mill Brook.  Water flows out of a dam from the southern end of Crystal Lake via the Suncook Lakes and Suncook River to the Merrimack River.  Shoreline development along Crystal Lake consists primarily of summer cottages, with a few year-round residents.  Belknap Mountain and Mount Major can be seen from the shoreline.

Stony Brook (Souhegan River): Stony Brook is a 10.6 mi river located in southern New Hampshire in the United States.  It is a tributary of the Souhegan River, which flows to the Merrimack River and ultimately to the Gulf of Maine.

Black Brook (Merrimack River): Black Brook is an 11.4 mi stream located in southern New Hampshire in the United States.  It is a tributary of the Merrimack River, which flows to the Gulf of Maine.

Still Brook Waterfall: Still Brook Waterfall is a waterfall at mouth of Still Brook, where the brook empties into Black Brook Cove, and so into the Atlantic Ocean.  Still Brook Waterfall flows onto Black Brook Beach, a popular swimming and picnic site on the Cabot Trail in the Cape Breton Highlands National Park, 10 km north of Ingonish, Nova Scotia, Canada.

Baboosic Brook: Baboosic Brook is a 12.7 mi stream located in southern New Hampshire in the United States.  It is a tributary of the Souhegan River, which flows to the Merrimack River and ultimately to the Gulf of Maine.

Black Brook (Chorley): Black Brook in Lancashire has its source at Great Hill in the West Pennine Moors.  The water is acidic due to a high level of peat in the uplands near to Round Loaf, giving the brook its brown colour.  The young river was known as Warth Brook in olden Heapey.  A feeder stream also known as Black Brook joins near Kittiwake Road - this short and weak water course commences at Eagle Tower.  The jointed brook feeds Anglezarke Reservoir, and joins the River Yarrow in lowland Chorley at Yarrow Bridge.  The entire course of Black Brook and the River Yarrow fall within Chorley and its villages.

Gulf of Maine: The Gulf of Maine (French: "Golfe du Maine" ) is a large gulf of the Atlantic Ocean on the east coast of North America.

Dublin Pond: Dublin Pond or Dublin Lake is a 236 acre water body located in Cheshire County in southwestern New Hampshire, United States, in the town of Dublin.  The pond lies at an elevation of 451 m above sea level, near the height of land between the Connecticut River/Long Island Sound watershed to the west and the Merrimack River/Gulf of Maine watershed to the east.  Water from Dublin Pond flows west through a series of lakes into Minnewawa Brook, a tributary of the Ashuelot River, which flows to the Connecticut River at Hinsdale, New Hampshire.  New Hampshire Route 101, a two-lane highway, runs along the northern shore of the lake, and the town center of Dublin is less than one mile to the east.

Supporting paragraphs: Black Brook (Merrimack River) Gulf of Maine
Answer: Atlantic Ocean